The Professional's Choice

The for loop is the most popular loop among C programmers because it bundles initialization, condition, and update into one concise, easy-to-read line.

Syntax

for (initialization; condition; update) {
    // block of code to run
}

Execution Flow - Exactly how it works:

1. Initialization runs only once at the very beginning.
2. Condition is checked. If it's False, the loop ends immediately.
3. If the condition is True, the Body of the loop is executed.
4. The Update step runs (e.g., i++).
5. Go back to Step 2.

Common Patterns

• Counting Up: for (int i = 0; i < 10; i++)
• Counting Down: for (int i = 10; i > 0; i--)
• Stepping: for (int i = 0; i < 100; i += 5) (0, 5, 10, 15...)
• Multiple variables: for (i = 0, j = 10; i < j; i++, j--)

Nested for Loops

This is how we handle 2D data like grids or images. The outer loop handles rows, and the inner loop handles columns.

for (int i = 1; i <= 3; i++) {       // Outer
    for (int j = 1; j <= 3; j++) {   // Inner
        printf("(%d,%d) ", i, j);
    }
    printf("\n");
}

The Empty For Loop

All parts of the for statement are optional.

• for(;;) is an infinite loop (same as while(1)).
• for(int i=0; i<10;) is valid as long as you update i inside the body.

In modern C (C99 and later), you should always declare the loop variable inside the for statement: for (int i = 0; ...). This is safer because the variable i is automatically destroyed when the loop ends, preventing you from accidentally using it elsewhere.