Demo: Run Once with do while

Run once, then check

A gate should report an attempt even when it has already reached its stopping value. An ordinary while could skip the report because it checks first. do ... while checks after the body, so it runs at least once. Its trailing while (condition); needs that semicolon.

Here attempt begins at the stop value. Predict the output:

#include <stdio.h>

int main(void) {
    int attempt = 3;
    do {
        printf("Attempt %d\n", attempt);
        attempt++;
    } while (attempt < 3);
    printf("Gate closed\n");
    return 0;
}

Start attempt at 1 and run it again: the body now gets more turns. Restore 3 afterward. The update still matters; a post-tested loop can run forever if its condition never becomes false.

Two loops, one inside the other

To label a grid, you can put for (int col = 0; col < 3; col++) inside for (int row = 0; row < 2; row++). The inner loop starts over for each row: three columns in each of two rows. break exits the nearest enclosing loop only; continue skips to that loop’s next iteration. Neither exits both loops for you. The next demo puts the grid into action.

Demo: Run Once with do while

Run once, then check

Here attempt begins at the stop value. Predict the output:

#include <stdio.h>

int main(void) {
    int attempt = 3;
    do {
        printf("Attempt %d\n", attempt);
        attempt++;
    } while (attempt < 3);
    printf("Gate closed\n");
    return 0;
}

Start attempt at 1 and run it again: the body now gets more turns. Restore 3 afterward. The update still matters; a post-tested loop can run forever if its condition never becomes false.