C++ Statements

A statement is the smallest complete instruction C++ executes, and a program is fundamentally a sequence of declaration, expression, and compound statements executed in order.

In this page:

What is a Statement?
Expression Statements
Compound Statements (Blocks)
Declaration Statements
Statement Termination with Semicolons

Syntax

cpp

type variable_name = value;   // declaration statement
variable_name = expression;  // expression statement
function_name(arguments);    // function call statement

What is a Statement?

A statement is the smallest complete instruction in C++ that the compiler executes, such as declaring a variable, calling a function, or evaluating an expression, and a C++ program is fundamentally a sequence of statements executed in order.

Example: What is a Statement?

cpp

#include <iostream>

int main() {
	int x = 5;             // declaration statement
	x = x + 1;              // expression statement
	std::cout << x;          // function call statement
	return 0;
}

Expression Statements

An expression statement consists of an expression, like an assignment or a function call, followed by a semicolon, and it's the most common kind of statement, executed purely for its side effect.

Example: Expression Statements

cpp

#include <iostream>

int main() {
	int total = 0;
	total = total + 10; // expression statement, executed for its side effect
	std::cout << total << std::endl;
	return 0;
}

Compound Statements (Blocks)

A compound statement, or block, groups multiple statements together inside curly braces, letting several statements be treated as a single unit wherever the language expects just one statement, such as inside an if or loop.

Example: Compound Statements (Blocks)

cpp

#include <iostream>

int main() {
	if (true) {
		int a = 1;
		int b = 2;
		std::cout << a + b << std::endl; // block treated as one statement
	}
	return 0;
}

Declaration Statements

A declaration statement introduces a new variable, specifying its type and name, and optionally an initial value, making that identifier available for use in the statements that follow.

Example: Declaration Statements

cpp

#include <iostream>

int main() {
	int score = 100; // declaration statement: type, name, initial value
	std::cout << score << std::endl;
	return 0;
}

Statement Termination with Semicolons

Every simple statement in C++, apart from compound statements enclosed in braces, must be terminated with a semicolon, which tells the compiler exactly where one instruction ends and the next one begins.

Example: Statement Termination with Semicolons

cpp

// Include std::cout and std::cin
#include <iostream>

// Program execution starts in main()
int main() {
	int a = 1; int b = 2;
	// Print to the console with cout
	std::cout << a + b << std::endl;
	// Return 0 to signal that the program finished successfully
	return 0;
}

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