### Python program to exchange the values of two numbers without using a third number :

In this example, we will learn *how to exchange two numbers without using any extra number*. We all know to exchange two numbers using a temporary number. But how to achieve this without using a third number? Let’s have a look :

### The algorithm to exchange two numbers without using the third number :

1. Get inputs of both numbers from the user. Store them in two *different* variables.

2. Add both numbers and store it in the *first number variable*.

3. Subtract the *second number* from the *first number* and store it in the *second number variable*.

4. Subtract again the *second number* from the *first number* ( the *second number* is changed to the *first number* in the third step above) and store it in the *first number variable*.

5. Now, both numbers are exchanged i.e. *first number variable* holds the second number and the *second number variable* holds the *first number*.

### Python program :

#1 first = int(input("Enter the value of the first number : ")) second = int(input("Enter the value of the second number : ")) #2 first = first + second #3 second = first - second #4 first = first - second #5 print("After exchange, First number is : ",first," Second number is : ",second)

### Explanation :

*The commented numbers in the above program denotes the step number below :*

1. Ask the user to enter the *first* and *second* number and store it in the variable *first* and *second*. For example, user entered *1* for *first* and *2* for *second*.

2. Add both *first* and *second* and assign the value to *first*. Now, *first* become *1 + 2 = 3*

3. Subtract *second* from *first* and store it in *second*. Now *second* is *3 – 2 = 1* i.e. the initial value of *first*.

4. Subtract *second* from *first* and store it in *first*. *first* become *3 – 1 = 2* i.e. the initial value of *second*.

5. Print out the final values of *first* and *second*.

### Examples :

Enter the value of the first number : 12 Enter the value of the second number : 23 After exchange, First number is : 23 Second number is : 12 Enter the value of the first number : 1 Enter the value of the second number : 2 After exchange, First number is : 2 Second number is : 1 Enter the value of the first number : 100 Enter the value of the second number : 200 After exchange, First number is : 200 Second number is : 100