C Logical Operators

Logical operators let you combine several true/false conditions into one. For example, you might want to run some code only if a user is logged in AND has permission. C gives you three logical operators to build these kinds of combined tests: AND, OR, and NOT.

The Logical Operators

The three logical operators work with true/false values. Remember that in C, any non-zero value counts as true and 0 counts as false. The result of a logical operator is always 1 or 0.

OperatorNameMeaningExample
&&Logical ANDTrue only if both sides are truex > 0 && x < 10
||Logical ORTrue if at least one side is truex == 0 || x == 100
!Logical NOTFlips true to false and back!(x > 5)

Using AND and OR

#include <stdio.h>

int main() {
  int age = 25;
  int hasTicket = 1;
  if (age >= 18 && hasTicket) {
    printf("You may enter.\n");
  }
  return 0;
}

The message only prints when both conditions are true: the person is at least 18 AND holds a ticket. If either one fails, the whole test is false and nothing prints.

The NOT Operator

The ! operator reverses a condition. If a value is true, ! makes it false, and if it is false, ! makes it true. It is handy for writing checks like only if the user is NOT banned.

Using NOT

#include <stdio.h>

int main() {
  int isRaining = 0;  // 0 means false
  if (!isRaining) {
    printf("Let's go outside!\n");
  }
  return 0;
}
Note: Do not confuse the logical operators && and || with the bitwise operators & and |. The single-character versions work on individual bits and behave very differently, so use the doubled symbols for true/false logic.
  • && is true only when both conditions are true.
  • || is true when at least one condition is true.
  • ! flips a condition from true to false or from false to true.

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