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cmathoperators
Shreyas Kotkar
Shreyas Kotkar

Reputation: 31

Increment & decrement operators in C

In the following program

     main()
 {
     int a = 21;
     int b = 10;
     int c ;
     c = a++; 
     printf("Value of c is %d\n", c );
     c = a--; 
     printf("Value of c is %d\n", c );
 }

the output is 

Value of c is 21
Value of c is 22

if we write just a++ it shows 22 and if we write a-- it shows 20 whereas when it is assigned to c as above it shows as 21 and 22 , why so?

Upvotes: 3

Views: 1234

Answers (4)

Rohit
Rohit

Reputation: 965

In case of a++, ++ is a postfix operator. So first value of a is assigned to c and then a is incremented.Hence value of c is 21.

Now the current value of a is 22. In case of c=a--, value of a(i.e 22 is assigned) to c and then a is decremented. Hence value of c is 22.

Upvotes: 2

Ren
Ren

Reputation: 2946

c=a++;
is equivalent to
c=a;a+=1;
andc=a--;
is equivalent to
c=a; a-=1;

Upvotes: 0

Amol Saindane
Amol Saindane

Reputation: 1598

There are postfix and prefix operators in C. When you use postfix operator then assignment happens first then operation. If you want to do assignment and operation in one line then you have to use prefix operator where operation happens first then assignment. If you modify your code as below then you will get expected output

     c = ++a; 
     printf("Value of c is %d\n", c );
     c = --a; 
     printf("Value of c is %d\n", c );

This link will give you more understanding

Upvotes: 0

Gopi
Gopi

Reputation: 19864

c = a++;

a++ means return the value of a and increment the value of a so

c = 21;/* Because a = 21 before incrementing */

a-- means the same return the value and decrement so

c = 22;

When we are at the line c = a--

a is 22 because of the previous a++ operation after this line a will be decremented and a will be 21.

Yes since you are assigning the value to c the value of a is returned to it before ++ or --

Upvotes: 1

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