The for loop

Learn to write counted loops with for and use a counter.

The for loop

The for loop is used to iterate a fixed number of times. It has three parts: initialization, condition and increment. They're separated by semicolons.

for (int i = 0; i < 5; i++) {
    printf("%d\n", i);
}

Here i starts at zero, increments by one each iteration, and the loop ends when i reaches 5. i++ means i = i + 1. Output: 0 1 2 3 4 (each on its own line).

Counting down

The counter doesn't have to go up. You can also count down; useful for countdowns or reverse iteration.

for (int i = 3; i > 0; i--) {
    printf("%d\n", i);
}
printf("Go!\n");

Here i-- decrements by one each iteration. Output: 3 2 1 Go!. Init, condition and increment must agree; otherwise the loop either never runs or runs forever.

Exercise Count from 1 to 5

Write a C program. Use a for (int i = 1; i <= 5; i++) loop to print each i with printf("%d\n", i);. Put #include <stdio.h> at the top.

Show example solution

#include <stdio.h>

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

Test yourself

How many times does for (int i=0; i<3; i++) run?
```
for (int i = 0; i < 3; i++) {
    printf("%d", i);
}
```
- 2 times
- 4 times
- 3 times
- Infinite
Show answer

3 times — Three iterations for i=0,1,2.

Write the increment

for (int i = 0; i < 5; ____) {
    printf("%d", i);
}

Show answer

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

Match the for parts

int i = 0

Init
i < 5

Condition
i++

Increment
{ }

Loop body

Next lesson: The while loop

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