C++ For Loop

A for loop is a loop that repeats a block with a counter in its header. The header holds the start, the condition, and the change.

Counting from zero

The counter starts at 0. The loop stops before the counter reaches 5.

#include <iostream>

int main() {
  for (int i = 0; i < 5; i++) {
    std::cout << i << std::endl;
  }
  return 0;
}

Stepping by two

The change part adds 2 after each run. The counter prints even numbers only.

#include <iostream>

int main() {
  for (int i = 0; i <= 8; i += 2) {
    std::cout << i << std::endl;
  }
  return 0;
}

Adding in a for loop

The total starts at 0. Each run adds the counter to the total.

#include <iostream>

int main() {
  int total = 0;
  for (int i = 1; i <= 4; i++) {
    total += i;
  }
  std::cout << total << std::endl;
  return 0;
}

Example

#include <iostream>

int main() {
  for (int i = 2; i <= 10; i += 2) {
    std::cout << i << std::endl;
  }
  return 0;
}

Key points

The for keyword starts the loop.
The header holds a start, a condition, and a change.
The start part runs once at the beginning.
The condition is checked before each run.
The change part runs after each run.

In this example, the counter starts at 2. The change part adds 2 after each run. The loop prints the even numbers up to 10.

Note

A for loop suits a count with a known start and end.

Try it Yourself

Edit the code, then press Run.

Running is simulated · Programiz C++ Compiler

#include <iostream>

int main() {
  for (int i = 2; i <= 10; i += 2) {
    std::cout << i << std::endl;
  }
  return 0;
}

Exercise

Which part of a for header runs after each run?

The start part The change part The condition The loop block