C++ Syntax & Program Structure

C++ programs follow a predictable structure: includes, optional namespace declarations, function definitions, and statements grouped in curly braces. Understanding this shape makes every future program easier to read.

Anatomy of a Program

At the top of a file, #include directives pull in library declarations you plan to use. The using namespace std; line (optional, and often avoided in larger projects) lets you write cout instead of std::cout. The rest of the file is made up of function definitions, with main() as the required starting point.

#include <iostream>
using namespace std;

// A simple function
int square(int n) {
    return n * n;
}

int main() {
    int result = square(5);
    cout << "5 squared is " << result << endl;
    return 0;
}

Statements, Blocks, and Comments

A statement is a single instruction, always ending in a semicolon. A block is a group of statements wrapped in curly braces { }, used for function bodies, loops, and conditionals. Comments are ignored by the compiler and exist purely to explain code to humans.

• // single line comment
• /* multi line comment */
• Whitespace and indentation are not required by the compiler, but consistent formatting is essential for readability.

Common Mistakes

• Placing using namespace std; inside header files, which can cause naming conflicts in larger projects.
• Mismatched curly braces — always count opens and closes, especially in nested blocks.
• Writing a comment with // that accidentally spans onto code you meant to keep active.
• Case-sensitivity mistakes — Cout is not the same identifier as cout.