C Logical Operators

The logical operators perform logical-AND (&&) and logical-OR ( || ) operations. 

Syntax

logical-AND-expression :

inclusive-OR-expression
logical-AND-expression && inclusive-OR-expression

logical-OR-expression :

logical-AND-expression
logical-OR-expression || logical-AND-expression

Logical operators do not perform the usual arithmetic conversions. Instead, they evaluate each operand in terms of its equivalence to 0. The result of a logical operation is either 0 or 1. The result’s type is int.

The C logical operators are described below:

The operands of logical-AND and logical-OR expressions are evaluated from left to right. If the value of the first operand is sufficient to determine the result of the operation, the second operand is not evaluated. This is called “short-circuit evaluation.” There is a sequence point after the first operand. 

Examples

The following examples illustrate the logical operators:

int w, x, y, z;

if ( x < y && y < z )

    printf( "x is less than z\n" );

In this example, the printf function is called to print a message if x is less than y and y is less than z. If x is greater than y, the second operand (y < z) is not evaluated and nothing is printed. Note that this could cause problems in cases where the second operand has side effects that are being relied on for some other reason.

printf( "%d" , (x == w || x == y || x == z) );

In this example, if x is equal to either w, y, or z, the second argument to the printf function evaluates to true and the value 1 is printed. Otherwise, it evaluates to false and the value 0 is printed. As soon as one of the conditions evaluates to true, evaluation ceases