Decimal roundoff error

[phatboy]

In my final calculation of my code, which is a mortgage calculator, I am getting no decimals. Should be an easy fix I just seem to be overlooking something. Thank you.

#include <iostream>
#include <iomanip>
#include <string>
#include <cmath>  
#include <limits> 


using namespace std;

 int main() {

   
    string again, x, y, z;
    double monthly_payment, total_payment;
    
    do
    {
        
        double x = valid_int("Loan Amount? ");				//loan amount

        double y = valid_int("Yearly Interest Rate? ");		//amount of loan interest

        int z = valid_int("Number of Years? ");				//life of the loan (in months)
        
        monthly_payment = calculate_mortgage(x,y,z);
        total_payment = monthly_payment*z*12;               ///****Trouble area******************
        
        cout << "Monthly Payment: " << monthly_payment << endl;
        cout << "Total Payment: " << total_payment << endl;
        
        cout << "More calculations? (yes/no) " << endl;
        cin >> again;
        
    }
    while (again== "yes");
        
        return 0;
}



double calculate_mortgage(double loan_amount, double yearly_rate, int num_years) {
    double monthly_payment = 0;
    
    double monthlyRate = (yearly_rate / 100.00) / 12 ;
    int numPayments = num_years * 12;
    
    monthly_payment = monthlyRate * pow((1 + monthlyRate), numPayments) / (pow((1+monthlyRate), numPayments) -1) * loan_amount;
    
    return monthly_payment;
}



int valid_int(string prompt) {
    double input;
    
    cout << prompt;
    cin >> input;
    
    // loop for a valid interger input
    // static_cast check if number is an integer (ie. double is not valid
    // cin.fail check if non numbers are entered
    while (input != static_cast<int>(input) || cin.fail()) {
        cin.clear(); //reset input error flag
        //get rid of invalid chars,
        cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
        cout << "Invalid input. Please input an integer.\n" << endl;
        cout << prompt; //reprompt input
        cin >> input;
    }
    // get rid any invalid characters after the valid number input
    // for example, if user entered, 102AB, the number will be 102 and
    // discard anything after 102
    cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
    return abs(input);
}

[TarikNeaj]

I'm confused as to why this even compiles? Your function are under main and you have no function protoypes, this shouldnt compile at all to my knowledge -

Declaring functions:
http://www.cplusplus.com/doc/tutorial/functions/

[phatboy]

Oops, my mistake. In my actual code I have the functions before main.

[phatboy]

The output that's giving me no decimals when I need them is on line 26. I'll remove the multiplication by 12 and my total_payment will give me 1 decimal place. I need 2 but this is close. I know that the 12 is causing something. Not sure still but I do need to multiply by 12 and need 2 decimal places for the total_payment variable.

[Peter87]

To make the code compile I had to add declarations for the two functions before main but when I run the program I'm not experiencing the problem you describe. Please test the code posted here, or post your real code.

Note that if the result is an integer (or very close) it will not show any decimals. If you always want to show two decimals you can use std::fixed and std::setprecision.

std::cout << std::fixed << std::setprecision(2);

[phatboy]

Thank you so much! I spent over an hour trying to figure out!! You're a life saver. Godspeed Peter87