Shortcuts and Type Casting

Update shortcuts

Changing a variable based on its old value is so common that C has shortcuts:

#include <stdio.h>

int main() {
    int coins = 10;
    coins += 5;
    printf("%d\n", coins);
    coins *= 2;
    printf("%d\n", coins);
    coins--;
    printf("%d\n", coins);
    return 0;
}

Output

15
30
29

Tip: ++ and -- are used all the time in loops (Module 5). Use them on a line of their own to keep things simple.

Type casting: changing the type

Sometimes you have two ints but want an exact decimal answer – for example an average. Write the type you want in brackets in front of a value. This is called a cast:

#include <stdio.h>

int main() {
    int total = 17;
    int count = 4;
    printf("Without cast: %d\n", total / count);
    printf("With cast: %.2f\n", (double) total / count);
    return 0;
}

Output

Without cast: 4
With cast: 4.25

(double) total turns 17 into 17.0 for this calculation, so the division keeps the decimals.

A cast also works the other way. (int) cuts off the decimal part:

#include <stdio.h>

int main() {
    double price = 19.99;
    int euros = (int) price;
    printf("%d\n", euros);
    return 0;
}

Output

19

Remember: (double) before a value makes division exact. (int) chops off the decimals.