帮帮忙吧各位大神们 小女子在线等了

#include "stdafx.h"
#include <math.h>
int _tmain(int argc, _TCHAR* argv[])
{
void payment(float,float,float);
int months;
float principal,rate,result;
printf("\n please enter your principal: "); /* this is the input section */
scanf_s("%f",&principal);
printf("\n please enter your month:");
scanf_s("%d",&months);
payment(principal,months,rate);
printf("Your payment:%7.2f",&result);
return 0;
}
void payment(float principal,int months,float rate)
{
float payment,result,rate;
rate=0.1/12;
result=payment=principal/1.0/rate-1.0/((rate*(1.0+rate)*pow((1.0+rate),months)));
}
不知道哪儿错了 怎么改呀帮帮忙