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What is a For Loop and Why is it Used?

A for loop is a control structure in programming that allows you to execute a specific block of code repeatedly. It’s especially useful when you want to perform the same task multiple times without duplicating your code. Let’s break down the essential components of a for loop:

1. Initialization: You declare and initialize a variable that serves as a counter. This step only happens once at the beginning.
2. Condition: You specify a condition that determines when the loop should stop executing.

Increment/Decrement: You define how the counter variable changes after each iteration.

Code:

#include <iostream>
using namespace std;

int main() {
    for (int i = 1; i <= 10; i++) {
        cout << "Hey, Striver, this is the " << i << "'th iteration" << endl;
    }
    return 0;
}

In this example, the loop will run ten times because it starts with i equal to 1, and the condition is met until i becomes 11 then the loop breaks. The variable i is incremented by 1 in each iteration.

1. Start: The process begins at the “start” point, indicating the beginning of the loop.
2. Initialize counter:  In this step, the loop control variable is initialised. This typically involves assigning an initial value to the counter. Usually denoted by the variable ‘i’
3. Condition check: The condition for the loop is checked in this stage. If the condition is evaluated as “true,” the loop continues to execute; otherwise, it terminates.
4. If the condition is “true,” the loop proceeds to execute the loop body and increment/decrement the counter.
5. After completing an iteration, the process returns to the “Condition check” step to re-evaluate the condition.
6. After executing the loop body, the counter is incremented or decremented. This step is crucial for controlling the loop’s termination.
7. The loop continues to execute as long as the condition remains “true.” Once the condition becomes “false,” the loop exits.
8. After exit from the loop, the code below the for-loop is executed and the program moves on.

Nested For Loops

Just like for loops, you can nest one for loop inside another. This concept becomes incredibly useful when you’re working with multi-dimensional data structures like a 2-D Array or need to solve complex problems involving multiple iterations.

Code:

#include <iostream>
using namespace std;

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

public class Main {
    public static void main(String[] args) {
        for (int i = 0; i < 3; i++) {
            for (int j = 0; j < 3; j++) {
                System.out.println("i = " + i + ", j = " + j);
                // Nested loop code
            }
        }
    }
}

Conditionals Inside For Loops

For loops are versatile; you can include conditional statements (if, else if, else) within them. This allows you to execute different code blocks based on certain conditions during each iteration.

for (int i = 1; i <= 10; i++) {
    if (i % 2 == 0) {
        // Code for even numbers
    } else {
        // Code for odd numbers
    }
}

Customising For Loops

You have flexibility in how you structure your for loop. For instance, you can customise the increment step to achieve specific patterns or iterate a certain number of times.

Code:

#include <iostream>
using namespace std;

int main() {
    for (int i = 1; i <= 25; i += 5) {
        cout << "i = " << i << endl;
    }
    return 0;
}

public class Main {
    public static void main(String[] args) {
        for (int i = 1; i <= 25; i += 5) {
            System.out.println("i = " + i);
        }
    }
}

In this example, i starts at 1 and increases by 5 in each iteration, resulting in five iterations.

Special thanks to Gauri Tomar for contributing to this article on takeUforward. If you also wish to share your knowledge with the takeUforward fam, please check out this article