The logical OR operator (||) returns the integral value 1 if either operand is nonzero; otherwise, it returns 0. Logical OR has left-to-right associativity.
Syntax
logical-or-expression :
logical-and-expression
logical-or-expression || logical-and-expression
The operands to the logical OR operator need not be of the same type, but they must be of integral or pointer type. The operands are commonly relational or equality expressions.
The first operand is completely evaluated and all side effects are completed before continuing evaluation of the logical OR expression.
The second operand is evaluated only if the first operand evaluates to false (0). This eliminates needless evaluation of the second operand when the logical OR expression is true.
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.