Basic problems with writing functions. Program randomly skips to the end - c++

Question

I'm very new to writing functions. This is my first attempt at using call by reference parameters specifically for a homework assignment. This program should calculate how long it takes to pay off a loan based on the users input of the amount they borrow, their monthly payment and the interest rate. The program should make sure the user doesnt input a payment number less than monthly interest amount and check for negative integers etc.
The area I commented out was my first go before i attempted to turn all of that into a function that uses call by reference parameters. At that point the program ran fine and i got output within a dollar of what I was looking for. After i rewrote the program like this and tried to make it a function, the program compiles but break to the bottom cout statements after asking for the interest rate. I assume my problem is somewhere within the interest1 function where i convert the percent to a decimal but i cant figure out why it would skip the rest of the functions afterwards.
Thanks for any advice you might have on this issue or anything else that looks wrong with the program itself.
#include <iostream>
#include <fstream>
using namespace std;
double amount();
double interest1();
double pay(double amt, double interest);
void payoff(double monthly, double Minpayment,double borrow,double interest, double&
totalinterest,int& month);
int main()
{
double monthly,month,totalinterest;
cout << fixed;
cout <<showpoint;
cout <<setprecision(2);
double borrow=amount();
double interest=interest1();
double Minpayment=pay(borrow, interest);
void payoff(double monthly,double Minpayment,double borrow,double interest,double&
totalinterest,int& month);
/*
// cout << "What is the monthly payment amount? \n";
// cin >> monthly;
// if(monthly<Minpayment)
// {
// cout << "You must make payments of at least: " << Minpayment++ << endl;
// cout << "Because your monthly payment is " << Minpayment << endl;
// cout << "Dont get overwhelmed with debt!!!!!! \n";
// }
// else
//
// {
// int month = 1;
// double totalinterest=0;
// do
// {
// double Minpayment=pay(borrow, interest);
// borrow=(borrow+Minpayment)-monthly;
// totalinterest=totalinterest+Minpayment;
// month++;
// }while(borrow>monthly);
*/
cout << "Your debt will be paid off in " << month << " months \n";
cout <<" with a final payment of " << borrow << endl;
cout << "You paid " << totalinterest << " in interest. \n";
return 0;
}
double amount()
{
double borrow,amt;
do
{
cout << "How much money do you want to borrow? \n";
cin >> amt;
if(amt<1)
cout << "You must enter a positive number!";
}while(amt<1);
borrow = amt;
return borrow;
}
double interest1()
{
double rate;
do
{
cout << "What is the annual interest rate expressed as a percent? \n";
cin >> rate;
if(rate<1)
cout << "You must enter a positive number!";
}while(rate<1);
double interest = (rate/12)*.01;
return interest;
}
double pay(double borrow,double interest)
{
double Minpayment=borrow*interest;
return Minpayment;
}
void payoff(double monthly,double Minpayment,double borrow,double interest, double&
totalinterest,int& month)
{
cout << "What is the monthly payment amount? \n";
cin >> monthly;
if(monthly<Minpayment)
{
cout << "You must make payments of at least: " << Minpayment++ << endl;
cout << "Because your monthly payment is " << Minpayment << endl;
cout << "Dont get overwhelmed with debt!!!!!! \n";
}
else
{
int month = 1;
do
{
double Minpayment=pay(borrow, interest);
borrow=(borrow+Minpayment)-monthly;
double totalinterest=totalinterest+Minpayment;
month++;
}while(borrow>monthly);
}
}

Answer 1

When you call a function inside main, you don't need to specify parameter types anymore:
void payoff(double monthly,double Minpayment,double borrow,double interest,double&
totalinterest,int& month); //wrong
should be
payoff(monthly, Minpayment,borrow, interest, totalinterest, month);
You should put double& andint& to the function's parameter list when define the function like you did.