C Input & Output

In C programming, input and output are core functionalities that allow your program to interact with users.

• Output: Display data using the printf() function.
• Input: Receive data using the scanf() function.

Both functions are defined in the standard input-output header:

c
#include <stdio.h>

The printf() function is used to print text or values on the screen.

c Run in compiler
#include <stdio.h>

int main() {
    printf("Hello World!");
    return 0;
}

Rules for printf()

• Text must be surrounded by double quotes " ".
• Omitting the quotes leads to a compilation error.

Correct:

c
printf("Hello");

Incorrect:

c
printf(Hello);

Multiple printf() Statements

You can use multiple printf() statements to print several lines.

c Run in compiler
#include <stdio.h> 
int main() 
{ 
printf("Hello World!"); 
printf("I am learning C.");
return 0; 
}

By default, printf() does not add a new line between outputs.

To print output on a new line, use the newline escape sequence \n. This moves the cursor to the beginning of the next line.

c Run in compiler
#include <stdio.h>
int main() 
{
printf("Hello World!\n"); 
printf("I am learning C.");
return 0;
}

Multiple Lines in Single printf()

You can print multiple lines using a single printf() statement by inserting \n where you want line breaks.

c Run in compiler
#include <stdio.h> 
int main()
{ 
printf("Hello World!\nI am learning C.\nAnd it is awesome!"); 
return 0;
}

Note: This method works, but using multiple printf() statements often makes code more readable.

Creating a Blank Line

To create a blank line between outputs, use two \n escape sequences.

c Run in compiler
#include <stdio.h> 
int main() 
{
printf("Hello World!\n\n"); 
printf("I am learning C.");
return 0; 
}

What is \n Exactly?

\n is called an escape sequence in C.

Escape sequences:

• Start with a backslash (\).
• Represent special characters.
• Help format output.

Specifically, \n moves the cursor to the next line.

Common Escape Sequences in C

Example Using Escape Sequences

c Run in compiler
#include <stdio.h>
int main() {
    printf("Hello\nWorld\n");
    printf("Hello\tWorld\n");
    printf("This is a backslash: \\\n");
    printf("She said \"Hello\"\n");
    return 0;
}

text
Hello
World
Hello	World
This is a backslash: \
She said "Hello"

The scanf() function is used to receive input from the user.

c Run in compiler
#include <stdio.h>
int main() 
{ 
int num; 
printf("Enter a number: "); 
scanf("%d", &num); 
printf("You entered: %d", num); 
return 0;
}

Rules for Using scanf()

• Use the correct format specifiers (%d, %f, %c, etc.).
• Always use & (address operator) before the variable name (except for strings).
• Input must match the variable's data type.

Common Format Specifiers in C

c Run in compiler
#include <stdio.h>
int main() {
    int num = 10;
    float pi = 3.14;
    char ch = 'A';
    char str[] = "Hello";

    printf("Integer: %d\n", num);
    printf("Float: %f\n", pi);
    printf("Character: %c\n", ch);
    printf("String: %s\n", str);

    return 0;
}

text
Integer: 10
Float: 3.140000
Character: A
String: Hello

• Forgetting & (address operator) in scanf() calls
• Using the wrong format specifier for the data type
• Omitting quotes in printf()
• Typing /n instead of \n for new lines

• printf() is used for output.
• scanf() is used for input.
• \n creates a new line.
• Escape sequences help format the output.
• Always include #include <stdio.h> at the start of your C programs.

1. printf() displays output, and scanf() accepts user input in C.
2. Always use the correct format specifiers for the variable types.
3. Escape sequences like \n and \t format the output for clarity.
4. Use & before variable names in scanf() (except for strings).
5. Missing quotes or incorrect format specifiers will result in errors.

1. Write a C program to input two numbers and print their sum.
2. Demonstrate the use of three different escape sequences in printf().
3. Create a program that reads a character and displays it back.
4. Modify a program to print output on three different lines using both single and multiple printf() statements.
5. Write a program that accepts a user's name as input and displays a welcome message.

1. Always match format specifiers with variable types in both printf() and scanf().
2. Use separate printf() statements for readability when printing multiple lines.
3. Remember to use \n for neat, readable output in the console.
4. Never forget the & operator for input variables in scanf(), except with strings.
5. Comment your code for clarity, especially when demonstrating input and output operations.