C++软件为什么编译这个程序时出错

double fz = 1.0;

#include<stdio.h>

int main()

{
    int N,i;
    double s;
    scanf("%d",&N);
double fz = 1.0;
for(i = 1; i <= N; i ++){
double t;
t = fz / i;
s += t;
}
printf("sum = %.6f\n", s);
getchar();
    return 0;
}

输入6
sum = 2.450000