Logical operators are used to compare or evaluate logical and relational expressions. The operands of these operators must produce either 1 (True) or 0 (False). The whole result produced by logical operators is thus either True or False.
Sometimes we need to ask more than one relational question at once.It let us combine two or more relational expressions into a single expression that evaluates to either true or false
It is also used in decision-making statements.
The below table shows the logical operators in C.
Operator
Symbol
Example
AND
&&
exp1 && exp2 e.g.(num>100)&&(num%2==0)
OR
||
exp1 || exp2 e.g.(num<100)||(num%2!=0)
NOT
!
!exp1 e.g.num!=5
Following table is C's logical operators in use:
Expression
What it evaluates to
(exp1 && exp2)
True(1) only if both exp1 and exp2 are true;
False(0) otherwise
(exp1 || exp2)
True(1) either exp1 or exp2 is true;
False(0) if only both are false
(!exp1)
True(1) if exp1 is false;
False(0) if exp1 is true
We can create expressions that use multiple logical operators. For example, to ask the question "Is x equal to 2, 3, or 4?" We can write : (x == 2) || (x == 3) || (x == 4)
It often provides more than one way to ask a question.
If x is an integer variable, the preceding question also could be written in either of the following ways:
1. (x > 1) && (x < 5)
2. (x >= 2) && (x <= 4)
Precedence of Logical Operators
Among the logical operators Not (!) has the highest precedence, AND (&&) has next highestandOR(||)haslowestprecedence.
The ! operator has a precedence equal to the unary mathematical operators ++ and --.
Thus, ! has a higher precedence than all the relational operators and all the binary mathematical operators.
The && and || operators have much lower precedence, lower than all the mathematical and relational operators, although, &&has a higher precedence than ||.
As with all of C's operators, parentheses can be used to modify the evaluation order when using the logical operators. Consider the following example:
We want to write a logical expression that makes three individual comparisons:
1. Is a less than b? 2. Is a less than c? 3. Is c less than d?
We want the entire logical expression to evaluate to true if condition 3 is true and if eithercondition 1orcondition 2istrue. Wecanwriteas a
However, this won't do what we intended. Because the && operator has higher precedence than ||, the expression is equivalent to a < b || (a < c && c < d) and evaluatestotrueif(a
So we need to write (a < b || a
Some examples
#include
#include
void main()
{
int a=10,b=5,c=20;
clrscr();
printf(“\n a %d”, (a printf(“\n a>b && b %d”, (a>b && b printf(“\n a %d”, (a printf(“\n a>b || b %d”, (a>b || b printf(“\n a>c || b>c => %d”, (a>c || b>c));
getch();
}
