task_3_exam

get n provided pmt,v and r

//  main.cpp
//  Final_Nanxing_Task3
//
//  Created by Nanxing LAI on 2019/1/20.
//  Copyright © 2019 Mac. All rights reserved.
//

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


using namespace std;

// the test of double value number, which inluding r, pmt and pv
double inputDouble(string prompt){
    cout << prompt;
    double value;
    cin >> value;
    
    while(value < 0){
        cout << "invalid, " << prompt;
        cin >> value;
    }
    return value;
}



int main()
{
    double r,pv,pmt,a,b,c,d;
    int n;
    // providing values
    r = inputDouble("please input periodic interest rate: ");
    pmt = inputDouble("please input the instalment: ");
    pv=inputDouble("plese input the present value:  ");
    
    n=1;
    a=pmt/pv;
    b=r*(1+1/(pow(1+r,n)-1));
    c=b-a;
    d=abs(c);
    while(d>0.001)
    {
        n=n+1;
        b=r*(1+1/(pow(1+r,n)-1));
        c=b-a;
        d=abs(c);
    }
    
    cout<<"the number of period is "<<n<<endl;
    return 0;
}