Variables, types, and arithmetic

Every value has a type

• In C, every variable has a type that says what kind of value it holds.
• The three you use most: int (a whole number), double (a number with a decimal point), and char (a single character).
• You must give the type when you create the variable: int n = 5; or double pi = 3.14;.

Doing arithmetic

• C does math with +, -, *, and /, just like a calculator.
• * and / happen before + and -. Use brackets ( ) to change the order.
• The % operator gives the remainder of a division: 17 % 5 is 2.

Integers divide differently

• When you divide two ints, C throws away the fraction: 7 / 2 is 3, not 3.5.
• To keep the fraction, at least one side must be a double. 7 / 2.0 is 3.5.
• You can cast an int to a double with (double): (double)sum / count.

Reading input

• scanf reads typed input into a variable. scanf("%d", &n); reads one int into n.
• Note the & before n: scanf needs the address of the variable so it can fill it in.
• In this playground, Run first asks you for the input, one value per line; Check answer feeds the example input for you.

#include <stdio.h>

int main(void) {
    int a = 7, b = 2;
    printf("%d\n", a / b);        // 3   (integer division)
    printf("%.1f\n", a / 2.0);    // 3.5 (one side is a double)
    printf("%d\n", a % b);        // 1   (remainder)
    return 0;
}

Common mistakes

• Declare a variable with its type: int n;.
• Integer division truncates: 7 / 2 is 3, not 3.5.

Now you try

• Use / and % for whole-number math, and a double (or a cast) when you need a fraction.
• For the function tasks, do not write a main — the checker provides one.
• Press Run to compile and run, then Check answer.