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Sunday, 22 April 2012

Logical operators in C

Logical operators are used to perform logical AND, OR and NOT operations.  It is used to connect one or more relational/conditional expressions to form a complex logical expression.  Any expression that evaluates to 0 is considered to be false and any expression that evaluates to non-zero value is considered to be true.

Logical operator example in C:
int x = 10, y = 20;
if ((x > 10) && (y > 10) {  // checks whether both the expressions are true
  printf("x and y are greater than 10");

if ((x > 10) || (y > 10) {  // checks whether atleast any one of the expression is true
  printf("any one or both x & y are greater than 10");

if (!(x > 10)) { // checks whether x is not greater than 10
        printf("x is not greater than 10");

Logical operators in C:
 Operator  Operation
 &&  logical AND
 ||  logical OR
 !  logical NOT

Below is the truth table for AND, OR and NOT logical operators.

Truth table for logical AND operator:

Operand1  Operand2  Result
 False False False
 False True False
 True False False
 True True True

Truth table for logical OR operator:

 Operand1 Operand2 Result
 False False False
 False True True
 True False True
 True True True

Truth table for logical NOT operator:

 Operand Result
 False True
 True False

Example C program using Logical Operators:
  #include <stdio.h>
  int main() {
        int a, b;
        printf("Enter two number: ");
        scanf("%d%d", &a, &b);
        if ((a > 100)  && (b > 100)) {
                printf("Both %d and %d are greater than 100\n", a, b);
                printf("Assigning 50 t0 b\n");
                b = 50;

        if ((b > 100) || (a > 100)) {
                printf("\nHitting Logical OR\n");
                printf("%d is greater than 100\n\n", a);

        if (!(b > 100)) {
                printf("%d is not greater than 100\n", b);
                printf("Hitting Logical NOT\n");
        return 0;

  jp@jp-VirtualBox:~/$ ./a.out
  Enter two number: 101 200
  Both 101 and 200 are greater than 100
  Assigning 50 t0 b

  Hitting Logical OR
  101 is greater than 100

  50 is not greater than 100
  Hitting Logical NOT

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