Swap two numbers without Using third variable in C

In this program we will swap two numbers without using third variable. Lets understand common ways to swap two numbers without using third variable:

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

First we will learn swapping of two numbers

Program 1: Using Third Variable 

Let's write a program in C to swap two numbers using third variable.

2. #include <stdio.h>
3. int main()
4. {
5.       double firstNumber, secondNumber, temporaryVariable;
6. 
   
7.       printf("Enter first number: ");
8.       scanf("%lf", &firstNumber);
9. 
   
10.       printf("Enter second number: ");
11.       scanf("%lf",&secondNumber);
12. 
    
13.       // Value of firstNumber is assigned to temporaryVariable
14.       temporaryVariable = firstNumber;
15. 
    
16.       // Value of secondNumber is assigned to firstNumber
17.       firstNumber = secondNumber;
18. 
    
19.       // Value of temporaryVariable (which contains the initial value of firstNumber) is assigned to secondNumber
20.       secondNumber = temporaryVariable;
21. 
    
22.       printf("\nAfter swapping, firstNumber = %.2lf\n", firstNumber);
23.       printf("After swapping, secondNumber = %.2lf", secondNumber);
24. 
    
25.       return 0;
26. }

Output:

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

Program 1: Using + and -

Let's write a program in C to swap two numbers without using third variable.

1. #include<stdio.h>  
2. #include<conio.h>  
3. main()  
4. {  
5. int a=10, b=20;    
6. clrscr();    
7. printf("Before swap a=%d b=%d",a,b);    
8.   
9. a=a+b;//a=30 (10+20)  
10. b=a-b;//b=10 (30-20)  
11. a=a-b;//a=20 (30-10)  
12.   
13. printf("\nAfter swap a=%d b=%d",a,b);  
14. getch();  
15. }  

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<conio.h>  
3. main()  
4. {  
5. int a=10, b=20;    
6. clrscr();    
7. printf("Before swap a=%d b=%d",a,b);    
8.   
9. a=a*b;//a=200 (10*20)  
10. b=a/b;//b=10 (200/20)  
11. a=a/b;//a=20 (200/10)  
12.   
13. printf("\nAfter swap a=%d b=%d",a,b);   
14. getch();  
15. }  

Output:

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