Work out a receipt

A receipt totals items before adding its fee. In C, *, /, and % take precedence over + and -; parentheses let you choose another order. % gives an integer remainder. Two integers divided with / produce an integer result, so 7 / 2 is 3, not 3.5. Use a floating-point operand such as 2.0 when you need a fraction.

For items * price + fee, multiply first. Check your prediction against this receipt:

#include <stdio.h>

int main(void) {
    int items = 3;
    int price = 4;
    int fee = 2;
    int total = items * price + fee;
    printf("Total: %d\n", total);
    return 0;
}

Change items and run again; the expression computes a new total. Division and remainder answer different questions about the same numbers:

#include <stdio.h>

int main(void) {
    int groups = 7 / 2;
    int leftover = 7 % 2;
    printf("Groups: %d, leftover: %d\n", groups, leftover);
    return 0;
}

7 / 2 makes three whole groups, and 7 % 2 leaves one over. Try predicting 3 + 2 * 4 (11), then (3 + 2) * 4 (20). Integer division truncates toward zero, including for negative results. Never divide by integer zero: its behavior is undefined. total += fee is shorthand for total = total + fee, but total still needs an initial value. The next demo converts an operand before division when a fraction matters.