Logical Operators in C

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Logical operators in C evaluate to either True or False. Logical operators are typically used with Boolean operands.

The logical AND operator (&&) and the logical OR operator (||) are both binary in nature (require two operands). The logical NOT operator (!) is a unary operator.

Since C treats "0" as False and any non-zero number as True, any operand to a logical operand is converted to a Boolean data.

Here is a table showing the logical operators in C −

The result of a logical operator follows the principle of Boolean algebra. The logical operators follow the following truth tables.

Logical AND (&&) Operator

The && operator in C acts as the logical AND operator. It has the following truth table −

The above truth table shows that the result of && is True only if both the operands are True.

Logical OR (||) Operator

C uses the double pipe symbol (||) as the logical OR operator. It has the following truth table −

The above truth table shows that the result of || operator is True when either of the operands is True, and False if both operands are false.

Logical NOT (!) Operator

The logical NOT ! operator negates the value of a Boolean operand. True becomes False, and False becomes True. Here is its truth table −

Unlike the other two logical operators && and ||, the logical NOT operator ! is a unary operator.

Example 1

The following example shows the usage of logical operators in C −

 #include <stdio.h> int main(){ int a = 5; int b = 20; if (a && b){ printf("Line 1 - Condition is true\n" ); } if (a || b){ printf("Line 2 - Condition is true\n" ); } /* lets change the value of a and b */ a = 0; b = 10; if (a && b){ printf("Line 3 - Condition is true\n" ); } else { printf("Line 3 - Condition is not true\n" ); } if (!(a && b)){ printf("Line 4 - Condition is true\n" ); } return 0; } 

Output

Run the code and check its output −

 Line 1 - Condition is true Line 2 - Condition is true Line 3 - Condition is not true Line 4 - Condition is true 

Example 2

In C, a char type is a subset of int type. Hence, logical operators can work with char type too.

 #include <stdio.h> int main(){ char a = 'a'; char b = '\0'; // Null character if (a && b){ printf("Line 1 - Condition is true\n" ); } if (a || b){ printf("Line 2 - Condition is true\n" ); } return 0; } 

Output

Run the code and check its output −

 Line 2 - Condition is true 

Logical operators are generally used to build a compound boolean expression. Along with relational operators, logical operators too are used in decision-control and looping statements in C.

Example 3

The following example shows a compound Boolean expression in a C program −

 #include <stdio.h> int main(){ int phy = 50; int maths = 60; if (phy < 50 || maths < 50){ printf("Result:Fail"); } else { printf("Result:Pass"); } return 0; } 

Output

 Result:Pass 

Example 4

The similar logic can also be expressed using the && operator as follows −

 #include <stdio.h> int main(){ int phy = 50; int maths = 60; if (phy >= 50 && maths >= 50){ printf("Result: Pass"); } else { printf("Result: Fail"); } return 0; } 

Output

Run the code and check its output −

 Result: Pass 

Example 5

The following C code employs the NOT operator in a while loop −

 #include <stdio.h> int main(){ int i = 0; while (!(i > 5)){ printf("i = %d\n", i); i++; } return 0; } 

Output

In the above code, the while loop continues to iterate till the expression "!(i > 5)" becomes false, which will be when the value of "i" becomes more than 5.

 i = 0 i = 1 i = 2 i = 3 i = 4 i = 5 

C has bitwise counterparts of the logical operators such as bitwise AND (&), bitwise OR (|), and binary NOT or complement (~) operator.