Logical Operators

Logical operators let you combine multiple conditions. Is this and that both true? Is either of them true? Is something not true? These operators work with boolean values — 1 for true, 0 for false.

The Three Logical Operators

• && — AND. True only if both sides are true.
• || — OR. True if at least one side is true.
• ! — NOT. Flips true to false and false to true.

Short-Circuit Evaluation

C is lazy in a good way. With &&, if the left side is false, C does not even evaluate the right side — the result is already false. With ||, if the left side is true, C skips the right side. This is called short-circuit evaluation, and it can prevent errors if used carefully.

#include 

int main() {
  int age = 25;
  int hasID = 1;

  if (age >= 18 && hasID) {
    printf("You can enter.\n");
  }

  int isWeekend = 0;
  int isHoliday = 1;

  if (isWeekend || isHoliday) {
    printf("No work today!\n");
  }

  printf("NOT isWeekend: %d\n", !isWeekend);
  return 0;
}