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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 −
Operator | Description | Example |
---|---|---|
&& | Called Logical AND operator. If both the operands are non-zero, then the condition becomes true. | (A && B) |
|| | Called Logical OR Operator. If any of the two operands is non-zero, then the condition becomes true. | (A || B) |
! | Called Logical NOT Operator. It is used to reverse the logical state of its operand. If a condition is true, then Logical NOT operator will make it false. | !(A) |
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 −
a | b | a&&b |
---|---|---|
true | true | True |
true | false | False |
false | true | False |
false | false | False |
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 −
a | b | a||b |
---|---|---|
true | true | True |
true | false | True |
false | true | true |
false | false | false |
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 −
A | !a |
---|---|
True | False |
False | True |
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 truen" ); } if (a || b){ printf("Line 2 - Condition is truen" ); } /* lets change the value of a and b */ a = 0; b = 10; if (a && b){ printf("Line 3 - Condition is truen" ); } else { printf("Line 3 - Condition is not truen" ); } if (!(a && b)){ printf("Line 4 - Condition is truen" ); } 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 = '' ''; // Null character if (a && b){ printf("Line 1 - Condition is truen" ); } if (a || b){ printf("Line 2 - Condition is truen" ); } 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 = %dn", 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.
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