Linux C 编程中segmentation fault (core dump)错误

Question

Linux C 小白，求大神指导，不胜感激。原代码在Windows下用VC++6.0编写，能正常运行，后复制到Ubuntu 12.04下，改了一部分命令，编译能通过，但在运行时报错segmentation fault (core dump)。下面为代码：
#include
#include
#include
#include
#include
double num;

int WriteDat(){

FILE *Data;

    const char *path1="/home/wanwan/Ai.txt";

    Data=fopen(path1,"a+");

printf("%lf\n",num); 

fprintf(Data,"%lf\n",num);

fclose(Data);

    return 1;

}

int main( ) {

FILE *fin;

int data1,data2,data3,data4 ;

int n,i;

    const char *path2="/home/wanwan/hotness.txt";

    fin = fopen(path2,"r");

for (i=0;i<37;i++){

    fscanf(fin,"%d %d %d %d", &data1, &data2, &data3, &data4); 

    num=0.001*data1+0.3*data2+0.2*data3+0.5*data4;

    WriteDat();

        }
    fclose(fin); 

            return 0;

}