Answer :

#include<stdio.h>   //header file contains the function,decleraction and macro defination of key words used in code.

int main ()

{

int num1,num2; //adressing the variables

num1=20;   //assining the values for variables

num2=10;    //assining the values for variables

printf("Before Swaining Num1 = %d and Num2=%d\n",num1,num2);//output

num1=num1+num2; // num1 =30  /*swaping the numbers without using the third variable.

                //swaping means interchanging the value of variables*/

num2=num1-num2; // num1= 20

num1=num1-num2;// 

printf("After Swaining Num1 = %d and Num2=%d\n",num1,num2);//output

}

Output :