Loops Control Structure Programs

C Loops Examples

loops are control structures that execute a set of statements repeatedly until a specified condition becomes false. They improve efficiency by eliminating code repetition and are essential for tasks like iteration, computation, and data processing. C supports for, while, and do-while loops, each suited for different use cases of iteration control.

76. C Program to Print 1 to N

#include <stdio.h>
int main(void){
    int n,i;
    printf("Enter N: ");
    scanf("%d",&n);
    for(i=1;i<=n;i++){
        printf("%d ",i);
    }
    return 0;
}

77. C Program to Print even Numbers up to N

#include <stdio.h>
int main(void){
    int n,i;
    printf("Enter N: ");
    scanf("%d",&n);
    for(i=2;i<=n;i+=2){
        printf("%d ",i);
    }
    return 0;
}

88. C Program to Print odd Numbers up to N

#include <stdio.h>
int main(void){
    int n,i;
    printf("Enter N: ");
    scanf("%d",&n);
    for(i=1;i<=n;i+=2){
        printf("%d ",i);
    }
    return 0;
}

89. C Program to Print Sum of first N Numbers

#include <stdio.h>
int main(void){
    int n,i,sum=0;
    printf("Enter N: ");
    scanf("%d",&n);
    for(i=1;i<=n;i++){
        sum+=i;
    }
    printf("Sum = %d\n",sum);
    return 0;
}

90. C Program to Print Factorial of a Number

#include <stdio.h>
int main(void){
    int n,i;
    long long fact=1;
    printf("Enter number: ");
    scanf("%d",&n);
    for(i=1;i<=n;i++){
        fact*=i;
    }
    printf("Factorial = %lld\n",fact);
    return 0;
}

91. C Program to Print Multiplication Table

#include <stdio.h>
int main(void){
    int n,i;
    printf("Enter number: ");
    scanf("%d",&n);
    for(i=1;i<=10;i++){
        printf("%d x %d = %d\n",n,i,n*i);
    }
    return 0;
}

92. C Program to Reverse a Number

#include <stdio.h>
int main(void){
    int n,rev=0,rem;
    printf("Enter number: ");
    scanf("%d",&n);
    while(n!=0){
        rem=n%10;
        rev=rev*10+rem;
        n/=10;
    }
    printf("Reverse = %d\n",rev);
    return 0;
}

93. C Program to Check Palindrome Number

#include <stdio.h>
int main(void){
    int n,rev=0,rem,temp;
    printf("Enter number: ");
    scanf("%d",&n);
    temp=n;
    while(n!=0){
        rem=n%10;
        rev=rev*10+rem;
        n/=10;
    }
    if(temp==rev){
        printf("Palindrome\n");
    }else{
        printf("Not palindrome\n");
    }
    return 0;
}

94. C Program to Check Armstrong Number

#include <stdio.h>
#include <math.h>
int main(void){
    int n,temp,digits=0,rem,sum=0;
    printf("Enter number: ");
    scanf("%d",&n);
    temp=n;
    while(temp!=0){
        digits++;
        temp/=10;
    }
    temp=n;
    while(temp!=0){
        rem=temp%10;
        sum+=pow(rem,digits);
        temp/=10;
    }
    if(sum==n){
        printf("Armstrong number\n");
    }else{
        printf("Not Armstrong\n");
    }
    return 0;
}

95. C Program to Count Digits in a Number

#include <stdio.h>
int main(void){
    int n,count=0;
    printf("Enter number: ");
    scanf("%d",&n);
    while(n!=0){
        n/=10;
        count++;
    }
    printf("Digits = %d\n",count);
    return 0;
}

96. C Program to Print Sum of Digits

#include <stdio.h>
int main(void){
    int n,sum=0;
    printf("Enter number: ");
    scanf("%d",&n);
    while(n!=0){
        sum+=n%10;
        n/=10;
    }
    printf("Sum = %d\n",sum);
    return 0;
}

97. C Program to Print Product of Digits

#include <stdio.h>
int main(void){
    int n,prod=1;
    printf("Enter number: ");
    scanf("%d",&n);
    while(n!=0){
        prod*=n%10;
        n/=10;
    }
    printf("Product = %d\n",prod);
    return 0;
}

98. C Program to Print Power using Loop

#include <stdio.h>
int main(void){
    int base,exp,i;
    long long power=1;
    printf("Enter base and exponent: ");
    scanf("%d%d",&base,&exp);
    for(i=1;i<=exp;i++){
        power*=base;
    }
    printf("Result = %lld\n",power);
    return 0;
}

99. C Program to Check Strong Number

#include <stdio.h>
int fact(int n){
    int i,f=1;
    for(i=1;i<=n;i++){
        f*=i;
    }
    return f;
}
int main(void){
    int n,temp,sum=0,rem;
    printf("Enter number: ");
    scanf("%d",&n);
    temp=n;
    while(n!=0){
        rem=n%10;
        sum+=fact(rem);
        n/=10;
    }
    if(sum==temp){
        printf("Strong number\n");
    }else{
        printf("Not Strong\n");
    }
    return 0;
}

100. C Program to Check Perfect Number

#include <stdio.h>
int main(void){
    int n,i,sum=0;
    printf("Enter number: ");
    scanf("%d",&n);
    for(i=1;i<n;i++){
        if(n%i==0){
            sum+=i;
        }
    }
    if(sum==n){
        printf("Perfect number\n");
    }else{
        printf("Not perfect\n");
    }
    return 0;
}

101. C Program to Print Fibonacci Series

#include <stdio.h>
int main(void){
    int n,a=0,b=1,c,i;
    printf("Enter terms: ");
    scanf("%d",&n);
    for(i=1;i<=n;i++){
        printf("%d ",a);
        c=a+b;
        a=b;
        b=c;
    }
    return 0;
}

102. C Program to Check Prime Number Check or Not

#include <stdio.h>
int main(void){
    int n,i,flag=0;
    printf("Enter number: ");
    scanf("%d",&n);
    if(n<=1){
        printf("Not prime\n");
        return 0;
    }
    for(i=2;i<=n/2;i++){
        if(n%i==0){
            flag=1;
            break;
        }
    }
    if(flag==0){
        printf("Prime\n");
    }else{
        printf("Not prime\n");
    }
    return 0;
}

103. C Program to Print Prime Numbers in a Range

#include <stdio.h>
int main(void){
    int i,j,n1,n2,flag;
    printf("Enter range: ");
    scanf("%d%d",&n1,&n2);
    for(i=n1;i<=n2;i++){
        if(i<2) continue;
        flag=0;
        for(j=2;j<=i/2;j++){
            if(i%j==0){
                flag=1;
                break;
            }
        }
        if(flag==0){
            printf("%d ",i);
        }
    }
    return 0;
}

104. C Program to Find LCM of Two Numbers

#include <stdio.h>
int main(void){
    int a,b,max;
    printf("Enter two numbers: ");
    scanf("%d%d",&a,&b);
    max=(a>b)?a:b;
    while(1){
        if(max%a==0 && max%b==0){
            printf("LCM = %d\n",max);
            break;
        }
        max++;
    }
    return 0;
}

105. C Program to Find GCD or HCF of Two Numbers

#include <stdio.h>
int main(void){
    int a,b;
    printf("Enter two numbers: ");
    scanf("%d%d",&a,&b);
    while(a!=b){
        if(a>b){
            a-=b;
        }else{
            b-=a;
        }
    }
    printf("GCD = %d\n",a);
    return 0;
}

106. C Program to Convert Decimal to Binary

#include <stdio.h>
int main(void){
    int n,b[32],i=0;
    printf("Enter decimal: ");
    scanf("%d",&n);
    while(n>0){
        b[i]=n%2;
        n/=2;
        i++;
    }
    printf("Binary = ");
    for(i=i-1;i>=0;i--){
        printf("%d",b[i]);
    }
    return 0;
}

107. C Program to Convert Binary to Decimal

#include <stdio.h>
int main(void){
    long bin;
    int dec=0,base=1,rem;
    printf("Enter binary: ");
    scanf("%ld",&bin);
    while(bin>0){
        rem=bin%10;
        dec+=rem*base;
        bin/=10;
        base*=2;
    }
    printf("Decimal = %d\n",dec);
    return 0;
}

108. C Program to Reverse Multiplication Table

#include <stdio.h>
int main(void){
    int n,i;
    printf("Enter number: ");
    scanf("%d",&n);
    for(i=10;i>=1;i--){
        printf("%d x %d = %d\n",n,i,n*i);
    }
    return 0;
}

109. C Program to Sum of Even and Odd Numbers Separately

#include <stdio.h>
int main(void){
    int n,i,even=0,odd=0;
    printf("Enter N: ");
    scanf("%d",&n);
    for(i=1;i<=n;i++){
        if(i%2==0){
            even+=i;
        }else{
            odd+=i;
        }
    }
    printf("Sum of even = %d\n",even);
    printf("Sum of odd = %d\n",odd);
    return 0;
}

110. C Program to Display Numbers Divisible by 3 and 5

#include <stdio.h>
int main(void){
    int n,i;
    printf("Enter N: ");
    scanf("%d",&n);
    for(i=1;i<=n;i++){
        if(i%3==0 && i%5==0){
            printf("%d ",i);
        }
    }
    return 0;
}

111. C Program to Print Numbers from 1 to N (do-while loop)

#include <stdio.h>   // Header file for input and output functions

int main(void) {     // Main function starts program execution

    int i = 1;       // Variable to control the loop, initialized to 1
    int n;           // Variable to store the user input value

    // Ask the user to enter the value of N
    printf("Enter the value of N: ");

    // Read the value of N from the input box
    scanf("%d", &n);

    // do-while loop executes at least once
    do {
        printf("%d ", i);   // Print the current value of i
        i++;                // Increment i by 1
    } while (i <= n);      // Loop continues while i is less than or equal to N

    return 0;               // End of the program
}

112. C Program to Print Numbers from N to 1 (do-while loop)

#include <stdio.h>   // Header file inclusion

int main(void) {

    int n;           // Variable to store user input

    // Take input from the user
    printf("Enter the value of N: ");
    scanf("%d", &n);

    // do-while loop to print numbers in reverse order
    do {
        printf("%d ", n);  // Print current value of n
        n--;               // Decrease n by 1
    } while (n >= 1);      // Loop runs until n becomes less than 1

    return 0;              // Program termination
}

113. C Program to Print Even Numbers up to N (do-while loop)

#include <stdio.h>   // Required for printf() and scanf()

int main(void) {

    int i = 2;       // Initialize i with first even number
    int n;           // Variable to store upper limit

    // Take input from the user
    printf("Enter the value of N: ");
    scanf("%d", &n);

    // do-while loop to print even numbers
    do {
        printf("%d ", i); // Print even number
        i = i + 2;        // Move to next even number
    } while (i <= n);    // Condition check

    return 0;             // End of program
}

114. C Program to Print Odd Numbers up to N (do-while loop)

#include <stdio.h>   // Header file for input-output

int main(void) {

    int i = 1;       // Start with first odd number
    int n;           // Variable to store input

    // Take input from user
    printf("Enter the value of N: ");
    scanf("%d", &n);

    // Loop to print odd numbers
    do {
        printf("%d ", i); // Print odd number
        i = i + 2;        // Increment by 2
    } while (i <= n);   // Loop condition

    return 0;             // Program ends
}

115. C Program to Find Sum of Numbers from 1 to N (do-while loop)

#include <stdio.h>   // Required for standard I/O functions

int main(void) {

    int i = 1;       // Loop counter initialization
    int n;           // Variable to store user input
    int sum = 0;     // Variable to store sum

    // Ask user to enter N
    printf("Enter the value of N: ");
    scanf("%d", &n);   // &n is HTML-safe display, shows &n on page

    // do-while loop to calculate sum
    do {
        sum = sum + i;  // Add current value of i to sum
        i++;            // Increment i
    } while (i <= n); 

    // Display the final sum
    printf("Sum = %d", sum);

    return 0;           // End of program
}

116. C Program to Print Multiplication Table of a Number (do-while loop)

#include <stdio.h>   // Header file for input-output

int main(void) {

    int num, i = 1;   // num = number to print table for, i = loop counter

    // Ask user to enter a number
    printf("Enter a number: ");
    scanf("%d", &num);  // HTML-safe display

    // Loop to print multiplication table from 1 to 10
    do {
        // Print current row: num x i = product
        printf("%d x %d = %d\n", num, i, num * i);
        i++;   // Increment counter
    } while (i <= 10); 

    return 0;   // End of program
}

117. C Program to Count Digits of a Number (do-while loop)

#include <stdio.h>

int main(void) {

    int num, count = 0;  // num = input number, count = number of digits

    // Ask user to enter a number
    printf("Enter a number: ");
    scanf("%d", &num);  // HTML-safe display

    // Loop to count digits
    do {
        count++;           // Increment digit counter
        num = num / 10;    // Remove last digit
    } while (num != 0);    // Loop until number becomes 0

    printf("Total digits = %d", count);  // Display total digits

    return 0;
}

118. C Program to Print Reverse a Number (do-while loop)

#include <stdio.h>

int main(void) {

    int num, rev = 0;   // num = input number, rev = reversed number

    // Ask user to enter a number
    printf("Enter a number: ");
    scanf("%d", &num);  // HTML-safe display

    // Loop to reverse the number
    do {
        rev = rev * 10 + num % 10;   // Extract last digit and add to rev
        num = num / 10;              // Remove last digit
    } while (num != 0);              // Repeat until number becomes 0

    printf("Reversed number = %d", rev);   // Display reversed number

    return 0;
}

119. C Program to Print Sum of Digits of a Number (do-while loop)

#include <stdio.h>

int main(void) {

    int num, sum = 0;   // num = input number, sum = sum of digits

    // Ask user to enter a number
    printf("Enter a number: ");
    scanf("%d", &num);  // HTML-safe display

    // Loop to calculate sum of digits
    do {
        sum = sum + num % 10;   // Add last digit to sum
        num = num / 10;          // Remove last digit
    } while (num != 0);          // Repeat until number becomes 0

    printf("Sum of digits = %d", sum);   // Display sum

    return 0;
}

120. C Program to Check Palindrome Number (do-while loop)

#include <stdio.h>

int main(void) {

    int num, temp, rev = 0;   // num = input number, temp = copy of num, rev = reversed

    // Ask user to enter a number
    printf("Enter a number: ");
    scanf("%d", &num);   // HTML-safe display

    temp = num;   // Copy num to temp

    // Loop to reverse the number
    do {
        rev = rev * 10 + temp % 10;   // Extract last digit and add to rev
        temp = temp / 10;              // Remove last digit
    } while (temp != 0);               // Repeat until temp becomes 0

    // Check if number is palindrome
    if (rev == num)
        printf("Palindrome number");
    else
        printf("Not a palindrome");

    return 0;
}

121. C Program to Find Factorial of a Number (do-while loop)

#include <stdio.h>

int main(void) {

    int n, fact = 1;   // n = input number, fact = factorial

    // Ask user to enter a number
    printf("Enter a number: ");
    scanf("%d", &n);   // HTML-safe display

    // Loop to calculate factorial
    do {
        fact = fact * n;  // Multiply current value of n to fact
        n--;              // Decrease n by 1
    } while (n > 0);     // Repeat until n > 0

    printf("Factorial = %d", fact);   // Display factorial

    return 0;
}

122. C Program to Print Fibonacci Series up to N Terms (do-while loop)

#include <stdio.h>

int main(void) {

    int n, i = 1;    // n = number of terms, i = counter
    int a = 0, b = 1, c;   // a = first term, b = second term, c = next term

    // Ask user to enter number of terms
    printf("Enter number of terms: ");
    scanf("%d", &n);   // HTML-safe display

    // Loop to generate Fibonacci series
    do {
        printf("%d ", a);     // Print current term
        c = a + b;            // Calculate next term
        a = b;                // Shift a
        b = c;                // Shift b
        i++;                  // Increment counter
    } while (i <= n);       // Repeat until N terms are printed

    return 0;
}

123. C Program to Print Uppercase Alphabets up to N (do-while loop)

#include <stdio.h>

int main(void) {

    int n;         // Number of alphabets to print
    char ch = 'A'; // Start character

    // Ask user to enter number of alphabets
    printf("Enter number of alphabets: ");
    scanf("%d", &n);   // HTML-safe display

    // Loop to print uppercase letters
    do {
        printf("%c ", ch);   // Print current alphabet
        ch++;                // Move to next alphabet
        n--;                 // Decrease remaining count
    } while (n > 0);       // Repeat until all alphabets are printed

    return 0;
}

124. C Program to Print Squares of Numbers up to N (do-while loop)

#include <stdio.h>

int main(void) {

    int i = 1, n;   // i = counter, n = limit

    // Ask user to enter limit N
    printf("Enter the value of N: ");
    scanf("%d", &n);   // HTML-safe display

    // Loop to print squares of numbers
    do {
        printf("Square of %d = %d\n", i, i * i);   // Display square
        i++;                                       // Increment counter
    } while (i <= n);   

    return 0;
}

125. C Program to Print Cubes of Numbers up to N (do-while loop)

#include <stdio.h>

int main(void) {

    int i = 1, n;   // i = counter, n = limit

    // Ask user to enter value of N
    printf("Enter the value of N: ");
    scanf("%d", &n);   // HTML-safe display

    // Loop to print cubes of numbers
    do {
        printf("Cube of %d = %d\n", i, i * i * i);   // Display cube
        i++;                                         // Increment counter
    } while (i <= n);                             

    return 0;
}

126. C Program to Print Numbers Divisible by 5 up to N (do-while loop)

#include <stdio.h>

int main(void) {

    int i = 5;   // Start with first number divisible by 5
    int n;       // Upper limit

    // Ask user to enter the value of N
    printf("Enter the value of N: ");
    scanf("%d", &n);   // HTML-safe display

    // Loop to print numbers divisible by 5
    do {
        printf("%d ", i);   // Display current number
        i += 5;             // Move to next number divisible by 5
    } while (i <= n); 

    return 0;
}

127. C Program to Print Numbers Divisible by 3 up to N (do-while loop)

#include <stdio.h>

int main(void) {

    int i = 3;   // Start with first number divisible by 3
    int n;       // Upper limit

    // Ask user to enter the value of N
    printf("Enter the value of N: ");
    scanf("%d", &n);   // HTML-safe display

    // Loop to print numbers divisible by 3
    do {
        printf("%d ", i);   // Display current number
        i += 3;             // Move to next number divisible by 3
    } while (i <= n); 

    return 0;
}

128. C Program to Print Input Until User Enters 0 (do-while loop)

#include <stdio.h>

int main(void) {

    int num;   // Variable to store user input

    // Loop will repeat until user enters 0
    do {
        printf("Enter a number (0 to stop): ");
        scanf("%d", &num);    // Read user input
    } while (num != 0);           // Continue if number is not 0

    printf("Program ended.");  // Optional message

    return 0;
}

129. C Program to Sum of Numbers Until Negative Number (do-while loop)

#include <stdio.h>

int main(void) {

    int num, sum = 0;   // num = input number, sum = total sum

    // Loop to keep adding positive numbers
    do {
        printf("Enter a number: ");
        scanf("%d", &num);       // Read input

        if (num >= 0)
            sum += num;              // Add only if number is positive

    } while (num >= 0);          // Repeat until a negative number is entered

    printf("Sum = %d", sum);         // Display total sum

    return 0;
}

130. C Program to Count Loop Executions Up to N (do-while loop)

#include <stdio.h>

int main(void) {

    int i = 1, n, count = 0;   // i = counter, n = limit, count = execution counter

    printf("Enter the value of N: ");
    scanf("%d", &n);

    // Loop to count number of executions
    do {
        count++;   // Increment execution count
        i++;       // Increment loop counter
    } while (i <= n); 

    printf("Loop executed %d times", count);   // Display result

    return 0;
}

131. C Program to Print ASCII Values from 0 to N (do-while loop)

#include <stdio.h>

int main(void) {

    int i = 0, n;   // i = counter, n = upper limit

    printf("Enter the value of N (ASCII limit): ");
    scanf("%d", &n);

    // Loop to print ASCII values
    do {
        printf("%c = %d\n", i, i);   // Display character and its ASCII value
        i++;                         // Increment counter
    } while (i <= n);         

    return 0;
}

132. C Program to Print Stars up to N (do-while loop)

#include <stdio.h>

int main(void) {

    int i = 1, n;   // i = counter, n = number of stars

    printf("Enter number of stars: ");
    scanf("%d", &n);

    // Loop to print stars
    do {
        printf("* ");  // Display a star
        i++;           // Increment counter
    } while (i <= n); 

    return 0;
}

133. C Program to Print Simple Menu Driven Program (do-while loop)

#include <stdio.h>

int main(void) {

    int choice;   // Variable to store user choice

    // Loop will repeat until user chooses option 3
    do {
        printf("\nMenu:\n1. Hello\n2. Hi\n3. Exit\n");
        printf("Enter your choice: ");
        scanf("%d", &choice);  // Read choice

        if (choice == 1)
            printf("Hello\n");
        else if (choice == 2)
            printf("Hi\n");

    } while (choice != 3);       // Loop ends when choice = 3

    printf("Program exited.");

    return 0;
}

134. C Program to Check Input Validation (Positive Number) (do-while loop)

#include <stdio.h>

int main(void) {

    int num;   // Variable to store user input

    // Loop will repeat until user enters a positive number
    do {
        printf("Enter a positive number: ");
        scanf("%d", &num);   // Read input
    } while (num <= 0);      // Continue if number is not positive

    printf("Valid number entered: %d", num);  // Display validated number

    return 0;
}

135. C Program to Find Max and Min Numbers (do-while loop)

#include <stdio.h>

int main(void) {
    int num, max, min;
    char choice;

    // Ask user to enter the first number
    printf("Enter a number: ");
    scanf("%d", &num);

    // Initialize max and min with the first number
    max = min = num;

    do {
        printf("Enter next number: ");
        scanf("%d", &num);

        // Update max and min
        if (num > max)
            max = num;
        if (num < min)
            min = num;

        // Ask user if they want to continue
        printf("Do you want to enter another number? (y/n): ");
        scanf(" %c", &choice);  // Space before %c to consume newline

    } while (choice == 'y' || choice == 'Y');

    // Display the results
    printf("Maximum number = %d\n", max);
    printf("Minimum number = %d\n", min);

    return 0;
}

136. C Program to Display Three Numbers in Sorted (Non-decreasing) Order

#include <stdio.h>

int main(void) {

    int a, b, c, temp;  // Variables to store three numbers and temporary variable for swapping

    // Ask user to enter three numbers
    printf("Enter three numbers: ");
    scanf("%d %d %d", &a, &b, &c);

    // Compare a and b, swap if a > b
    if (a > b) {
        temp = a;
        a = b;
        b = temp;
    }

    // Compare a and c, swap if a > c
    if (a > c) {
        temp = a;
        a = c;
        c = temp;
    }

    // Compare b and c, swap if b > c
    if (b > c) {
        temp = b;
        b = c;
        c = temp;
    }

    // Display numbers in sorted order
    printf("Numbers in non-decreasing order: %d %d %d\n", a, b, c);

    return 0;  // End of program
}

137. C Program to Display Number, Square, and Cube in Tabular Format

#include <stdio.h>

int main(void) {

    int i = 1;   // Loop counter
    int n;       // Variable to store user input

    // Ask user to enter a positive integer
    printf("Enter a positive integer (n ≥ 0): ");
    scanf("%d", &n);

    // Validate input
    if (n < 0) {
        printf("Invalid input! Please enter n ≥ 0.\n");
        return 0;   // Exit program if input is invalid
    }

    // Print table header
    printf("Number\tSquare\tCube\n");   // \t adds tab spacing

    // Loop to calculate and display number, square, and cube
    do {
        printf("%d\t%d\t%d\n", i, i * i, i * i * i);  // Print current number, square, and cube
        i++;   // Increment counter
    } while (i <= n);  

    return 0;  // End of program
}

138. C Program to Demonstrate the use of relational operators

#include <stdio.h>

int main(void) {

    int a, b;   // Variables to store user input

    // Ask user to enter two numbers
    printf("Enter first number (a): ");
    scanf("%d", &a);

    printf("Enter second number (b): ");
    scanf("%d", &b);

    // Demonstrate relational operators

    printf("\nRelational Operator Demonstration:\n");

    // Equal to (==)
    if (a == b)
        printf("%d == %d : True\n", a, b);
    else
        printf("%d == %d : False\n", a, b);

    // Not equal to (!=)
    if (a != b)
        printf("%d != %d : True\n", a, b);
    else
        printf("%d != %d : False\n", a, b);

    // Greater than (>)
    if (a > b)
        printf("%d > %d : True\n", a, b);
    else
        printf("%d > %d : False\n", a, b);

    // Less than (<)
    if (a < b)
        printf("%d < %d : True\n", a, b);
    else
        printf("%d < %d : False\n", a, b);

    // Greater than or equal to (>=)
    if (a >= b)
        printf("%d >= %d : True\n", a, b);
    else
        printf("%d >= %d : False\n", a, b);

    // Less than or equal to (<=)
    if (a <= b)
        printf("%d <= %d : True\n", a, b);
    else
        printf("%d <= %d : False\n", a, b);

    return 0;  // End of program
}

139. C Program to Check Amicable Numbers

//Amicable numbers are a pair of numbers where each number is equal to the sum of the proper divisors of the other number.

//Proper divisors of a number = all divisors except the number itself.

//Consider the numbers 220 and 284:

//Proper divisors of 220: 1, 2, 4, 5, 10, 11, 20, 22, 44, 55, 110 | Sum = 284

//Proper divisors of 284: 1, 2, 4, 71, 142 | Sum = 220

#include <stdio.h>

int main(void) {

    int num1, num2;      // Variables to store input numbers
    int sum1 = 0, sum2 = 0;  // Variables to store sum of divisors
    int i;               // Loop counter

    // Ask user to enter two numbers
    printf("Enter first number: ");
    scanf("%d", &num1);

    printf("Enter second number: ");
    scanf("%d", &num2);

    // Find sum of proper divisors of num1
    for (i = 1; i <= num1 / 2; i++) {
        if (num1 % i == 0) {
            sum1 += i;   // Add divisor to sum1
        }
    }

    // Find sum of proper divisors of num2
    for (i = 1; i <= num2 / 2; i++) {
        if (num2 % i == 0) {
            sum2 += i;   // Add divisor to sum2
        }
    }

    // Check if the numbers are Amicable
    if (sum1 == num2 && sum2 == num1)
        printf("%d and %d are Amicable Numbers.\n", num1, num2);
    else
        printf("%d and %d are NOT Amicable Numbers.\n", num1, num2);

    return 0;  // End of program
}

140. C Program to Generate Prime Numbers up to N (Using For Loop)

#include <stdio.h>

int main(void) {

    int n;       // Upper limit for prime numbers
    int i, j;    // Loop counters
    int isPrime; // Flag to check if number is prime

    // Take input from user
    printf("Enter a positive integer (n ≥ 2): ");
    scanf("%d", &n);

    // Validate input
    if (n < 2) {
        printf("No prime numbers available.\n");
        return 0;  // Exit program if n < 2
    }

    printf("Prime numbers up to %d:\n", n);

    // Loop through numbers from 2 to n
    for (i = 2; i <= n; i++) {
        isPrime = 1;  // Assume number is prime

        // Check divisibility from 2 to i/2
        for (j = 2; j <= i / 2; j++) {
            if (i % j == 0) { // If divisible
                isPrime = 0;  // Not a prime number
                break;        // Exit inner loop
            }
        }

        // If number is prime, print it
        if (isPrime)
            printf("%d ", i);
    }

    return 0;  // End of program
}

141. C Program to Calculate nCr (Combinations)

#include <stdio.h>

// Function to calculate factorial of a number
long long factorial(int num) {
    long long fact = 1;
    int i;

    for (i = 1; i <= num; i++) {
        fact = fact * i;
    }

    return fact;
}

int main(void) {

    int n, r;               // Variables to store user input
    long long nFact, rFact, nMinusRFact;  // Factorials of n, r, and (n-r)
    long long nCr;           // Result

    // Take input from user
    printf("Enter value of n: ");
    scanf("%d", &n);

    printf("Enter value of r: ");
    scanf("%d", &r);

    // Validate input
    if (r > n || n < 0 || r < 0) {
        printf("Invalid input! Make sure 0 ≤ r ≤ n.\n");
        return 0;
    }

    // Calculate factorials
    nFact = factorial(n);               // n!
    rFact = factorial(r);               // r!
    nMinusRFact = factorial(n - r);     // (n-r)!

    // Calculate nCr
    nCr = nFact / (rFact * nMinusRFact);

    // Display result
    printf("C(%d, %d) = %lld\n", n, r, nCr);

    return 0;  // End of program
}

142. C Program to Calculate nPr (Permutation)

#include <stdio.h>

// Function to calculate factorial of a number
long long factorial(int num) {
    long long fact = 1;
    int i;

    for (i = 1; i <= num; i++) {
        fact = fact * i;   // Multiply each number from 1 to num
    }

    return fact;
}

int main(void) {

    int n, r;                 // Variables to store user input
    long long nFact, nMinusRFact;  // Factorials of n and (n-r)
    long long nPr;             // Result of permutation

    // Take input from user
    printf("Enter value of n: ");
    scanf("%d", &n);

    printf("Enter value of r: ");
    scanf("%d", &r);

    // Validate input
    if (r > n || n < 0 || r < 0) {
        printf("Invalid input! Make sure 0 ≤ r ≤ n.\n");
        return 0;
    }

    // Calculate factorials
    nFact = factorial(n);           // n!
    nMinusRFact = factorial(n - r); // (n-r)!

    // Calculate nPr
    nPr = nFact / nMinusRFact;

    // Display result
    printf("P(%d, %d) = %lld\n", n, r, nPr);

    return 0;  // End of program
}

143. C Program to Generate First n Terms of Cosine Series

#include <stdio.h>
#include <math.h>

// Function to calculate factorial
long long factorial(int num) {
    long long fact = 1;
    int i;
    for (i = 1; i <= num; i++) {
        fact = fact * i;
    }
    return fact;
}

int main(void) {

    int n, i;         // n = number of terms, i = counter
    double x, term;   // x = angle in radians, term = current term
    double cosx = 0;  // Sum of cosine series
    int sign = 1;     // Alternating sign for each term (+1, -1, +1, ...)

    // Input angle and number of terms
    printf("Enter the value of x (in radians): ");
    scanf("%lf", &x);

    printf("Enter the number of terms: ");
    scanf("%d", &n);

    printf("\nCosine Series Terms:\n");

    // Loop to generate series terms
    for (i = 0; i < n; i++) {
        term = sign * (pow(x, 2 * i) / factorial(2 * i));  // Calculate term: x^(2i) / (2i)!
        cosx += term;     // Add term to sum
        printf("Term %d: %.6lf\n", i + 1, term); // Display current term
        sign = -sign;     // Alternate the sign for next term
    }

    // Display final value of cos(x)
    printf("\nApproximate value of cos(%.2lf) using %d terms: %.6lf\n", x, n, cosx);

    return 0;
}

144. C Program to Display Number in Text Form

#include <stdio.h>

int main(void) {

    int num, temp, reversed = 0;   // num = input, temp = copy, reversed = reversed number
    int digit;                      // To extract digits

    // Array to store text for digits 0-9
    char *digitsText[] = {
        "ZERO", "ONE", "TWO", "THREE", "FOUR",
        "FIVE", "SIX", "SEVEN", "EIGHT", "NINE"
    };

    // Ask user to enter a positive number
    printf("Enter a positive integer: ");
    scanf("%d", &num);

    if (num < 0) {
        printf("Invalid input! Enter a positive integer.\n");
        return 0; // Exit program
    }

    // Reverse the number to maintain original order
    temp = num;
    if (num == 0) {   // Special case for 0
        printf("%s\n", digitsText[0]);
        return 0;
    }

    while (temp > 0) {
        reversed = reversed * 10 + temp % 10;  // Build reversed number
        temp /= 10;                             // Remove last digit
    }

    // Print each digit in text form
    printf("Number in text form: ");
    while (reversed > 0) {
        digit = reversed % 10;                  // Extract last digit
        printf("%s ", digitsText[digit]);       // Print corresponding text
        reversed /= 10;                          // Remove last digit
    }

    printf("\n");

    return 0;  // End of program
}

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