Tính tổng n giai thừa - C/C++

#include <stdio.h>

#include <conio.h>

int GiaiThua(int x)

{

    if(x<0) return x;

    if(x==1) return 1;

    else return (x*GiaiThua(x-1));

}

int main()

{   printf("*************************************");

    printf("\n CHUONG TRINH TINH TONG N GIAI THUA");

    printf("\n*************************************");

    int i,n;

    int tong,giai_thua,tran;

    tong = 0;

    giai_thua = 1;

    do{

        printf("\nNhap vao so n: ");

        scanf("%d",&n);

    }while(n<=0);

    for (i=1;i<=n;i++)

    {

        giai_thua = GiaiThua(i);

        if(giai_thua<0)

        {

            printf(" => Tran bo nho tai i = %d",i);

            break;

        }

        tran = tong;

        tong = tong + giai_thua;

        if(tong<0)

        {

            printf(" => Tran bo nho tai i = %d",i);

            tong = tran;

            break;

        }

    }

    printf("\n\nTong can tinh la: %ld",tong);

    getch();

    return 0;

}