C Operators

C operators are symbols that perform operations on values and variables, such as adding numbers or comparing them. This lesson covers the operators you will use every day.

Arithmetic Operators

C has + - * / and % (remainder). Dividing two integers gives an integer: the fractional part is thrown away.

#include <stdio.h>

int main(void) {
    int a = 17, b = 5;
    printf("%d %d %d\n", a + b, a - b, a * b);
    printf("%d %d\n", a / b, a % b);
    printf("%.1f\n", (double)a / b);
    return 0;
}

22 12 85
3 2
3.4

Assignment and Increment

Compound operators like += and *= update a variable in place. ++ adds one and -- subtracts one. x++ uses the old value then increments; ++x increments first.

#include <stdio.h>

int main(void) {
    int x = 10;
    x += 5;   // 15
    x *= 2;   // 30
    int y = x++;  // y = 30, x = 31
    int z = ++x;  // x = 32, z = 32
    printf("x=%d y=%d z=%d\n", x, y, z);
    return 0;
}

x=32 y=30 z=32

Comparison and Logical Operators

Comparisons (== != < > <= >=) return 1 for true and 0 for false. Logical operators combine them: && (and), || (or), ! (not).

#include <stdio.h>

int main(void) {
    int age = 20;
    int hasTicket = 1;
    printf("%d\n", age >= 18);
    printf("%d\n", age >= 18 && hasTicket);
    printf("%d\n", !hasTicket);
    return 0;
}

1
1
0

Operator Precedence

• *, / and % run before + and -.
• Comparisons run before && and ||, and && runs before ||.
• Assignment (=) has very low precedence.
• When in doubt, add parentheses: they make intent clear.
• Do not confuse = (assign) with == (compare); compile with -Wall to catch it.

Frequently asked questions

Why does 5 / 2 equal 2 in C?

Both operands are int, so C performs integer division and drops the fraction. Make one operand a double, for example 5.0 / 2, to get 2.5.

What is the difference between i++ and ++i in C?

Both add one to i. i++ evaluates to the old value, while ++i evaluates to the new value. On their own line they behave the same.

What does the % operator do in C?

It returns the remainder of integer division. For example 17 % 5 is 2. It is often used to test if a number is even (n % 2 == 0).