我也不知道为什么就编译失败了??

#include<iostream>
using namespace std;
int plus1(unsigned long long &a,unsigned long long &b)
{
	unsigned long long t=0;
	t=a+b;
}
int main()
{
	unsigned long long c,d;
	scanf("%llu%llu",&c,&d);
	plus1(c,d);
	printf("%llu",t);
	return 0;
}