For Loop

In programming, loops are used to repeat a block of code multiple times. This is helpful when you want to perform the same task again and again without writing the same code repeatedly.

Types of Loops

for loop – when you know how many times to run
while loop – when you don't know how many times, but you want to repeat while a condition is true
do-while loop – similar to while loop, but it runs at least once

The for loop is one of the most commonly used loops in C programming. It's perfect when you know exactly how many times you want to repeat a block of code. Think of it like setting a timer - you decide how many times something should happen, and the loop takes care of the counting for you!

Syntax

for (initialization; condition; increment/decrement) {
    // Code to be executed
}

The for loop has three parts separated by semicolons:

Initialization: Sets up a counter variable (executed once at the beginning)
Condition: Checked before each iteration (loop continues while true)
Increment/Decrement: Updates the counter after each iteration

How It Works

Here's a simple example that prints numbers from 1 to 5:

#include <stdio.h>

int main() {
    for (int i = 1; i <= 5; i++) {
        printf("%d ", i);
    }
    return 0;
}

Output: 1 2 3 4 5

Let's break down what happens:

int i = 1 - Initialize counter i to 1
i <= 5 - Check if i is less than or equal to 5
If true, execute printf("%d ", i)
i++ - Increment i by 1
Repeat steps 2-4 until condition becomes false

Common Patterns

Counting Up

// Print numbers 0 to 9
for (int i = 0; i < 10; i++) {
    printf("%d ", i);
}

Counting Down

// Print numbers 10 to 1
for (int i = 10; i >= 1; i--) {
    printf("%d ", i);
}

Custom Increments

// Print even numbers from 0 to 10
for (int i = 0; i <= 10; i += 2) {
    printf("%d ", i);
}

Multiplication Table

Printing Multiplication Tables is a very good real world use case to understand the importance of loops. Following code prints the 5 table.

#include <stdio.h>

int main() {
    int num = 5;
    
    printf("Multiplication table of %d:\n\n", num);
    for (int i = 1; i <= 10; i++) {
        printf("%d x %d = %d\n", num, i, num * i);
    }
    
    return 0;
}

This print the following

Multiplication table of 5:
5 x 1 = 5
5 x 2 = 10
5 x 3 = 15
5 x 4 = 20
5 x 5 = 25
5 x 6 = 30
5 x 7 = 35
5 x 8 = 40
5 x 9 = 45
5 x 10 = 50

Key Points to Remember

The loop variable (i in our examples) is often called a counter or iterator
You can use any variable name, but i, j, k are common conventions
The initialization happens only once, but condition and increment happen every iteration
If the condition is false from the start, the loop body won't execute at all
Be careful with the condition to avoid infinite loops!

Loops Introduction