Read the three parts of a for loop separately: what happens once at the start, when the loop continues, and what changes after each iteration.
Count from 1 to 5
for (int i = 1; i <= 5; i++) {
printf("%d\n", i);
}The initialization runs once. The condition is checked before each iteration, and the update runs after the body.
Counting down
for (int i = 5; i > 0; i--) {
printf("%d\n", i);
}This prints 5, 4, 3, 2, 1. The condition means “continue while i is greater than zero.” Use i >= 0 to include zero. Trace the value, condition, and output on paper for the first three iterations.
Run these snippets inside main with stdio.h included, using C99 or later.