关于条件语句

#include<stdio.h>
void main()
{
int a,b,c;
printf("please input a and b: ");
scanf("%d%d",a,b);
c=a-b;
if(c==a||c==b)
printf("difference is equal to value<number of value entered>\n");
else
printf("difference is not equal to any of the values entered\n");
}
程序要求：计算两个数的差值。如果差值等于输入的两个值中的任意一个，
输出：difference is equal to value<number of value entered>如果差值
不等于输入的两个值中的任意一个，
输出：difference is not equal to any of the values entered
我不知问题出在哪，请大家指教！