Basic question -5 (swapping values without using third variable )

How to Swap values of 2 variable without using third variable .
It is to simple If  we use third variable .

Let  variable are 'a' , 'b' , 'temp' . we have swap value  of variable 'a' & 'b'.  & 'temp' is third variable .

          temp = a
               a = b
          b  = temp

 Now solve it without using third variabe

       a = a + b
       b = a - b
       a = a - b

C Program :

           Without  Using third variable :

 #include<stdio.h>  
 void swap(int *p,int *q)  
 {          // operation to swap  
       *p=*p+*q;  
       *q=*p-*q;  
       *p=*p-*q;  
      printf(" \n reverse volue\n a=%d b=%d",*p,*q);  
 }  
 main()  
 {  
   int a,b;  
      printf("enter volue of a & b : ");  
      scanf("\n%d %d",&a,&b);  
      swap(&a,&b);  
 }  

OUTPUT :

Using Third Variable :

 #include<stdio.h>  
 void swap(int *p,int *q)  
 {          // operation to swap  
       int temp;  // temp variabe  
       temp = *p;  
        *p = *q;  
        *q = temp;  
      printf(" \n reverse volue\n a=%d b=%d",*p,*q);  
 }  
 main()  
 {  
   int a,b;  
      printf("enter volue of a & b : ");  
      scanf("\n%d %d",&a,&b);  
      swap(&a,&b);  
 }