C programming language has logical operators for logical expressions. The output of a logical operation is a Boolean value – true or false.
In a logical expression, you have one or more operands and each has a truth value, depending on the truth value of each operand the logical operator decides the final truth value of the logical expression.
Logical Operators
A list of logical operators in C language is given below. The minimum numbers of operands required by each of the operators are also given in the same table.
- AND (&&)
- OR (||)
- NOT (!)
We shall discuss each of them in more detail now.
AND (&&) operator
The AND operation is denoted by two ‘ampersand’ symbol. To understand the AND operation, consider the following expression,
A && B
Where A = (3 < 4) and B = (10 < 20)
The final output of the expression depends on the following conditions.
A is true && B is true = A && B is true
A is false && B is true = A && B is false.
A is true && B is false = A && B is false.
A is false && B is false = A && B is false.
So, the AND is only true when both A and B are true.
OR (||) operator
The OR operation is also useful logical operator in the C language. The value of the expression is true under the following conditions.
A is true || B is true = A || B is true
A is false || B is true = A || B is true
A is true || B is false = A || B is true
A is false || B is false = A || B is false
From the above example, it is clear that the OR is only true when at least A or B is true.
NOT (!) operator
The NOT is called the negation operation. It negates the truth value of the existing expression.
For example,
if A is true, then ! A is false
If A is false, then ! A is true.
Note:- The !(!A) == A.
Example – AND, OR, NOT
/* C Program to demonstrate use of Logical Operators */
#include <stdio.h>
int main() {
int A, B ;
A = (5 < 10); /* True */
B = (10 < 20); /* True */
printf("\n\n\n\n\n");
/* Working of AND operation - both A and B must be true */
if(A && B) {
printf("\tOutput AND - both A and B are true\n\n");
}
/* Operation of Not operator */
A = (2 < 10); /* False */
B = (4 < 8); /* True */
/* A && B is False */
if(!(A && B)) {
printf("\tOutput NOT - (A && B) is False so negation !(A && B) is True\n\n");
}
/* Working of OR operator - any one of A or B must be true */
if (A || B) {
printf("\tOutput OR - Any one of A or B is true\n\n");
}
getch();
return 0;
}
Output – AND, OR, NOT
References
- Balagurusamy, E. 2000. Programming in ANSI C. Tata McGraw-Hill Education,
- Brian W. Kernighan, Dennis M. Ritchie. 1988. C Programming Language, 2nd Edition. Prentice Hall.
- Kanetkar, Yashavant. 20 November 2002. Let us C. Bpb Publications.