Swap two variable value within one line statement using c program

#include<stdio.h>
void main()
{
    int a=10;

    int b=20;

    printf("a value is = %d    b value is = %d \n",a,b);

    a = ( a + b ) - ( b = a );

    printf("a value is = %d    b value is = %d \n",a,b);

}