C++ Syntax

Every C++ program follows this skeleton:

cpp Run in compiler
#include <iostream>      // 1. Headers
using namespace std;     // 2. (Optional) namespace alias

int main() {             // 3. Entry function
    // 4. Statements go here
    cout << "Hi";
    return 0;            // 5. Exit code
}

A statement is one instruction. Every C++ statement ends with a semicolon ;.

cpp
int x = 10;          // statement 1
cout << x << endl;   // statement 2

Forgetting ; is the #1 beginner error — expected ';' before '}'.

Code surrounded by { } is a block. Functions, loops, ifs, classes — all use blocks.

cpp
if (x > 0) {
    cout << "positive";
    cout << " number";
}

Two flavours:

cpp
// Single-line comment

/* Multi-line
   comment */

Comments are ignored by the compiler. Use them to explain why, not what.

C++ is case-sensitive:

cpp
int Age = 21;
cout << age;  // ERROR — 'age' not declared (it's 'Age')

• Start with a letter or underscore: score, _total, userName.
• Can contain letters, digits, underscores: score1, total_amount.
• Cannot start with a digit: ❌ 1score.
• Cannot be a keyword: ❌ int, ❌ return.

int, float, double, char, bool, void, if, else, for, while, do, switch, break, continue, return, class, struct, public, private, protected, new, delete, this, const, static, namespace, using, template, typename.

cpp
cout << "Hello";              // print text
cout << 42;                   // print number
cout << "Sum = " << 10+5;     // chain
cout << endl;                  // newline + flush
cout << "\n";                  // newline (faster)

cpp
int age;
cout << "Enter age: ";
cin >> age;                    // read integer
cout << "You are " << age;

cpp Run in compiler
#include <iostream>
using namespace std;

int main() {
    string name;
    int age;

    cout << "Name? ";
    cin >> name;
    cout << "Age? ";
    cin >> age;

    cout << "Hello " << name << ", you are " << age << " years old." << endl;
    return 0;
}

Output (for input Aarav 21):

Hello Aarav, you are 21 years old.

• Missing semicolon — cout << "Hi" without ; triggers a confusing compiler error on the next line.
• Wrong arrow direction — cin << age; (wrong, should be cin >> age).
• Reading without #include <string> — using string requires <string> (or transitive include via <iostream>).
• Identifier starts with digit — int 1count; won't compile.
• Mismatched braces — every { needs a }; missing one breaks the entire file.

1. Sum two numbers — Read two integers with cin and print their sum. Hint: int a, b; cin >> a >> b;.
2. Fix the bugs — cout << Hello; (missing quotes) and cin << x; (wrong direction). Hint: strings need "...", cin uses >>.
3. Echo your name — Read a string name and print Hello, NAME!. Hint: include <string>, declare string name;.
4. Comment cleanup — Take any 10-line C++ snippet and add // comments explaining each line. Hint: comments make code readable for the next person.

Think Like a Programmer: Syntax is the grammar of code. Get it wrong and the compiler refuses to talk to you. Get it right and the compiler becomes your friendliest teacher — its error messages will guide every fix.