C OPERATOR UNIT 3 PART 3

LOGICAL OPERATOR

Introduction

You can combine results of multiple relations or logical operations by using logical operation. The logical operators are negation (!), logical AND (&&), and logical OR (||), in the same order of preference.

Program

#include<stdio.h>

main( )

{

  int c1,c2,c3;

printf("ENTER VALUES OF c1, c2 AND c3");

scanf("%d%d%d",&c1.&c2,&c3);

 if((c1 < c2)&&(c1<c3))

  printf("\n c1 is less than c2 and c3");

if (!(c1< c2))

 printf("\n c1 is greater than c2");

if ((c1 < c2)||(c1 < c3))

 printf("\n c1 is less than c2 or c3 or both");

}

Input

c1= 2;

c2= 3;

c3= 4;

Output

ENTER VALUES OF c1, c2 AND c3

2

3

4

c1 is less than c2 and c3

c1 is less than c2 or c3 or both

Explanation

1. Logical AND returns a true value if both relational expressions are true. Logical OR returns true if any of the expressions are true. Negations return complements of values of relational expressions, as shown in Table 3.2.

Table 3.2: Results of AND, OR, and Negation.
R1	R2	R1 && R2	R1 || R2	! R1
T	T	T	T	F
T	F	F	T	F
F	T	F	T	T
F	F	F	F	T

2. Logical operators AND, and OR have higher priority than assignment operators, but less than relational operators. Negation operators have the same priority as unary operators, that is, the highest priority.
3. While evaluating logical expressions, C uses the technique of short circuiting. So if the expression is:       C1 && C2 && C3 && C4 if C1 is true then only C2 is evaluated. If C1 is false, the expression returns false even if C2, C3, and C4 are true. So if C1 is false C2, C3, and C4 are not evaluated. Remember this when you are doing something such as searching in an array. For example, if you want to search for K in an array, the last value of which is subscript N, you can write the search condition in two ways:

I - (a [i] == K) && (i <= N)

II - (i <= N) && (a[i] == K)

4. In case I you compare the array limit with K and check the bound. This is not correct because if the value of i is more than N you will get the array index out-of-bounds error.
5. In case II, you first check the bound and then compare the array element. This is correct because you will never compare the array element if value of i is more than N.The technique of short-circuiting is applicable to the OR operator also. Thus if the expression is:

C1 || C2 || C3 || C4 if C1 is true then the expression returns true and C2, C3 and C4 are not evaluated.

TERNARY OPERATOR

Introduction

Ternary operators return values based on the outcomes of relational expressions. For example, if you want to return the value of 1 if the expression is true and 2 if it is false, you can use the ternary operator.

Program/Example

If you want to assign the maximum values of i and j to k then you can write the statement

k = ( i>j ) ? i : j;

If i > j then k will get the value equal to i, otherwise it will get the value equal to j.

The general form of the ternary operator is:

(expr 1) ? expr2 : expr3

If expr1 returns true then the value of expr2 is returned as a result; otherwise the value of expr3 is returned.

INCREMENT OPERATOR

Introduction

You can increment or decrement the value of variable using the increment or decrement operator. These operators can be applied only to variables and they can be applied using prefix form or postfix form.

Program

#include<stdio.h>

main( )

{

int I,j,k;

i = 3;

j =4;

k = i++ + --j;

printf("i = %d, j = %d, k = %d",i,j,k);

}

Input

i =3, j = 4.

Output

i = 4, j = 3, k = 6.

Explanation

When the prefix form is used, the value of the variable is incremented/decremented first and then applied. In the postfix form, the value is applied and only after the assignment operator is done is the value incremented or decremented.

1. Suppose you write

2.  i = 3;

3.  j =4;

4.  k = i++ + -j;

you will get the value of k as 6, i as 4 and j as 3. The order of evaluation is as follows:

1. i gets the value 3.
2. j is decremented to 3.
3. k gets the value 3 + 3.
4. i is incremented.
4. Suppose you write

6.  i = 5;

7.  i = i++ * i++

Then you will get the value of i as 27. This is because first the value 5 is used as to make i = 25 and then i is incremented twice. The increment and decrement operators have higher priority than the arithmetic operators.