for Loop

The for loop is a control structure that is used to execute a block of code a specific number of times. It is typically used when the number of iterations is known beforehand, making it an ideal choice for counting or iterating through arrays or collections.

Syntax of for Loop

for (initialization; condition; update) {
    // Code to execute repeatedly
}

• Initialization: Initializes the loop control variable(s). It is executed only once, at the start of the loop.
• Condition: Evaluated before each iteration. If true, the loop continues; if false, the loop ends.
• Update: Modifies the loop control variable(s) after each iteration.

How It Works

1. Initialization is executed.
2. The Condition is checked:
   • If true, the loop body executes.
   • If false, the loop exits.
3. The Update is executed after the loop body.
4. Steps 2 and 3 repeat until the condition becomes false.

Example: Basic for Loop

#include <iostream>
using namespace std;

int main() {
    for (int i = 1; i <= 5; i++) {
        cout << "Iteration: " << i << endl;
    }
    return 0;
}

Output:

Iteration: 1
Iteration: 2
Iteration: 3
Iteration: 4
Iteration: 5

Using a for Loop with Arrays

The for loop is commonly used to iterate over arrays:

#include <iostream>
using namespace std;

int main() {
    int numbers[] = {10, 20, 30, 40, 50};

    for (int i = 0; i < 5; i++) {
        cout << "Element at index " << i << ": " << numbers[i] << endl;
    }

    return 0;
}

Output:

Element at index 0: 10
Element at index 1: 20
Element at index 2: 30
Element at index 3: 40
Element at index 4: 50

Infinite for Loop

A for loop can run indefinitely if the condition is always true. This can be intentional in cases where a break statement is used to exit the loop dynamically:

#include <iostream>
using namespace std;

int main() {
    for (;;) {
        cout << "This is an infinite loop!" << endl;
        break; // Prevents actual infinite execution
    }
    return 0;
}

Nested for Loops

You can nest for loops to handle multi-dimensional data or complex scenarios:

#include <iostream>
using namespace std;

int main() {
    for (int i = 1; i <= 3; i++) {
        for (int j = 1; j <= 3; j++) {
            cout << "(" << i << ", " << j << ") ";
        }
        cout << endl;
    }
    return 0;
}

Output:

(1, 1) (1, 2) (1, 3)
(2, 1) (2, 2) (2, 3)
(3, 1) (3, 2) (3, 3)

Modifying Control Flow

break Statement: Exits the loop prematurely.

for (int i = 1; i <= 5; i++) {
    if (i == 3) break;
    cout << i << " ";
}
// Output: 1 2

continue Statement: Skips the current iteration.

for (int i = 1; i <= 5; i++) {
    if (i == 3) continue;
    cout << i << " ";
}
// Output: 1 2 4 5

Example: Sum of First n Numbers

#include <iostream>
using namespace std;

int main() {
    int n, sum = 0;

    cout << "Enter a positive number: ";
    cin >> n;

    for (int i = 1; i <= n; i++) {
        sum += i;
    }

    cout << "Sum of first " << n << " numbers is: " << sum << endl;
    return 0;
}

Input:

5

Output:

Sum of first 5 numbers is: 15

for Loop Variations

Multiple Variables in Initialization:

for (int i = 0, j = 5; i < 5; i++, j--) {
    cout << i << " + " << j << endl;
}

Skipping Initialization or Update:

int i = 0;
for (; i < 5;) {
    cout << i << endl;
    i++;
}

Reverse Looping:

for (int i = 5; i > 0; i--) {
    cout << i << " ";
}
// Output: 5 4 3 2 1