Logical Operators

Logical Operators

Logical operators combine true/false values into one decision: && (AND), || (OR), and ! (NOT).

AND: both must be true

1 && 1 is the only AND that is true:

• 1 && 1 -> 1
• 1 && 0 -> 0
• 0 && 1 -> 0
• 0 && 0 -> 0

OR: at least one must be true

• 1 || 1 -> 1
• 1 || 0 -> 1
• 0 || 1 -> 1
• 0 || 0 -> 0

NOT flips the value

• !1 -> 0
• !0 -> 1

Examples

int raining = 1;
int holiday = 0;

printf("%d\n", raining && holiday);  // 0
printf("%d\n", raining || holiday);  // 1
printf("%d\n", !raining);             // 0

Short-circuit evaluation

For a && b, if a is already 0, the result is 0 - so b is never even evaluated. For a || b, if a is 1, b is skipped.

TL;DR

• && is true only when both sides are true.
• || is true when at least one side is true.
• ! flips true to false and false to true.
• C short-circuits: it skips the rest when it already knows the answer.