C++ For Loop Control Structure

Introduction

In programming, loops let you repeat tasks efficiently. In C++, the for loop is used when you know in advance how many times you want the loop to run (or can express it numerically). This makes for loops ideal for fixed-count iterations, arrays, traversals, and more.

Syntax of the For Loop in C++

for (init; condition; increment) {
    // statements to repeat
}

for (init; condition; increment) {
    // statements to repeat
}

• init: executed once at the start (often used to initialize loop counter).
• condition: evaluated before every iteration; if true, loop body executes; if false, loop ends.
• increment: executed at the end of each iteration (often used to update loop counter).

Working / Flow of the For Loop

1. init runs once.
2. Test condition.
   • If true → execute loop body → then increment → back to step 2.
   • If false → exit loop and continue after the loop.

#include <iostream>
using namespace std;

int main() {
    int x = 5;
    for (int i = 1; i <= 10; i++) {
        // Printing 5’s multiplication table
        cout << x << " x " << i << " = " << (x * i) << endl;
    }
    return 0;
}

#include <iostream>
using namespace std;

int main() {
    int x = 5;
    for (int i = 1; i <= 10; i++) {
        // Printing 5’s multiplication table
        cout << x << " x " << i << " = " << (x * i) << endl;
    }
    return 0;
}

Example: Multiplication Table using For Loop

Output:

5 x 1 = 5  
5 x 2 = 10  
5 x 3 = 15  
…  
5 x 10 = 50  

5 x 1 = 5  
5 x 2 = 10  
5 x 3 = 15  
…  
5 x 10 = 50  

Explanation

• The loop starts with i = 1.
• Checks i <= 10 → true, enters body.
• Prints 5 x i = result.
• After printing, i++ increments i.
• Loops until i = 11, where i <= 10 is false → exit loop.

Variations & Advanced Uses

• Multiple init or increment expressions: for (int i = 0, j = 10; i < j; i++, j--) { // do something }
• Omitting parts (rarely recommended):
  You can omit init, condition, or increment (but then you must handle them inside the loop to avoid infinite loops). int i = 0; for ( ; i < 5; ) { cout << i << " "; i++; }
• Infinite loop using for: for ( ;; ) { // runs forever until break or return }

When to Use For vs While vs Do-While

• Use for loop when you know (or can calculate) how many times you need to loop.
• Use while loop when the termination condition depends on external constraints or inputs.
• Use do-while when you always want the loop body to execute at least once.

Tips & Best Practices

• Always use braces {} even for single-line bodies — avoids errors when you extend the loop later.
• Avoid modifying the loop variable inside the body in unexpected ways — keep increment clear.
• Don’t let loops run too long (watch out for off-by-one errors).
• Use break or continue carefully inside for loops (you may refer to jump statements post).