C Program to swap two numbers without third variable

We can swap two numbers without using third variable. There are two common ways to swap two numbers without using third variable:

1. By + and -
2. By * and /

Program 1: Using + and -

Let's see a simple c example to swap two numbers without using third variable.

1. #include<stdio.h>  
2.  int main()    
3. {    
4. int a=10, b=20;      
5. printf("Before swap a=%d b=%d",a,b);      
6. a=a+b;//a=30 (10+20)    
7. b=a-b;//b=10 (30-20)    
8. a=a-b;//a=20 (30-10)    
9. printf("\nAfter swap a=%d b=%d",a,b);    
10. return 0;  
11. }   

Output:

Before swap a=10 b=20
After swap a=20 b=10

Program 2: Using * and /

Let's see another example to swap two numbers using * and /.

1. #include<stdio.h>  
2. #include<stdlib.h>  
3.  int main()    
4. {    
5. int a=10, b=20;      
6. printf("Before swap a=%d b=%d",a,b);       
7. a=a*b;//a=200 (10*20)    
8. b=a/b;//b=10 (200/20)    
9. a=a/b;//a=20 (200/10)    
10.  system("cls");  
11. printf("\nAfter swap a=%d b=%d",a,b);       
12. return 0;  
13. }   

Output:

Before swap a=10 b=20
After swap a=20 b=10