In this tutorial, we are going to learn a new program which is a simple program and most commonly used in exams or in interviews that is **Swap two numbers without using third variable**.

**How to swap two numbers without using third variable?**

For swapping number first we have two numbers and without using third variable we swap numbers by doing a simple mathematical operation (sum and subtract )

## Steps for swapping of two numbers

Let us assume variable **a, b**

1. Add first and second number and store addition in the first variable.

**a = a + b**

2. Subtract first and second number and store it in the second variable.

** b = a – b**

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

** a = a – b**

**Example:**

a = 10, b = 20;

a = 10+20

a= 30

b = 30-20

**b = 10**

a = 30-10

**a=20**

**Result a = 20, b = 10;**

## C Program to swap two numbers without using third variable

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#include<stdio.h> void main() { int first,second ; printf("Enter first\n"); scanf("%d",&first); printf("Enter second\n"); scanf("%d",&second); printf("before swaping\n first =%d \n second =%d\n"first, second); first = first + second; second = first - second; first = first - second; printf(" after swaping\n first=%d\n second=%d",first,second); } |

**Output:**

**Explanation**:

**1. First Here we initialized the first and second variable.**

first —> for storing 1st number

second –>for storing the second number

**2. Now here goes the logic(let us take first = 10 and second=20)**

first = first + second , Therefore, first =10+20 =30

second = first – second , Therefore second = 30 – 20 =10

first = first – second, Therefore first =30 – 10 = 20

**3. Now the values of first and second are 20 and 10**

**4. The values of the first and second are printed.**

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