下面c程序 double total = 0.0; 这一句为何放在第四行可以，而在放在第八行就不行，

#include <stdio.h>

int main(void)
{
    const double unit_price = 3.50;
   // double total = 0.0; //放在这里就可以
    int quantity = 0;
    printf("Enter the number that you want to buy:");
    scanf("%d", &quantity);
   double total = 0.0; //为何放在这里不行
    if(quantity > 10)
        total = quantity*unit_price*0.95;
    else
        total = quantity*unit_price;
    printf("The price for %d is $%.2f\n", quantity, total);
    return 0;