Converting issue in C#

Question

I keep getting an error message stating that I cannot convert a string to a double in reference to line 39. Can someone review the code and let me know where I'm off? I feel that maybe line 25 should list double for the variable "R."

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace Present_Value
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        //Declare global variables. 
       /* double F = int.Parse(futureTextBox.Text);
        double R = int.Parse(interestTextBox.Text);
        double N = int.Parse(sitTextBox.Text);*/

        private double CalculateData(int F, int R, int N)
        {
            double P = F/(1 + R)*N;
            return P ;

        }



        private void button1_Click(object sender, EventArgs e)
        {

            int n = int.Parse(sitTextBox.Text);
            int f = int.Parse(futureTextBox.Text);
            int r = double.Parse(intTextBox.Text);

            presentValuelabel.Text = CalculateData(f,r,n).ToString();
        }

        private void Form1_Load(object sender, EventArgs e)
        {

        }

        private void exitButton_Click(object sender, EventArgs e)
        {
            //Close this form.
                this.Close();
        }
    }
}

You're declaring int variable but trying to assign double with double.Parse() method. Try to change double.Parse() to int.Parse(). — Batın Evirgen
– Batın Evirgen, Commented Jun 18, 2017 at 23:19
Which is line 39 and line 25? You should post a minimal reproducible example and make it easy for us to answer. — Enigmativity
– Enigmativity, Commented Jun 19, 2017 at 0:05
Do keep in mind that the calculation F/(1 + R)*N (as it stands in your question) is purely being calculated with integer math. So, for example, the result of (1 / (1 + 2) * 3) is 0 using integer math. But if I change to doubles then (1.0 / (1.0 + 2.0) * 3.0) gives 1.0. — Enigmativity
– Enigmativity, Commented Jun 19, 2017 at 0:09

Tien Nguyen Ngoc · Accepted Answer · 2017-06-18 23:41:32Z

1

There are two way to edit.

Method 1) You should edit CalculateData function. int R => double R

private double CalculateData(int F, double R, int N)
{
    double P = F / (1 + R) * N;
    return P;

}
private void button1_Click(object sender, EventArgs e)
    {

        int n = int.Parse(sitTextBox.Text);
        int f = int.Parse(futureTextBox.Text);
        double r = double.Parse(intTextBox.Text);

        presentValuelabel.Text = CalculateData(f, r, n).ToString();
    }

Method 2) You should edit button1_Click function. double.Parse(intTextBox.Text) => int.Parse(intTextBox.Text)

private void button1_Click(object sender, EventArgs e)
{

    int n = int.Parse(sitTextBox.Text);
    int f = int.Parse(futureTextBox.Text);
    int r = int.Parse(intTextBox.Text);

    presentValuelabel.Text = CalculateData(f, r, n).ToString();
}

I hope it will help you.

edited Jun 18, 2017 at 23:41

answered Jun 18, 2017 at 23:32

Tien Nguyen Ngoc

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Comments

Patrick Ribbing · Accepted Answer · 2017-06-19 07:53:57Z

0

When dealing with user input (from the textboxes) you should use the .TryParse() methods instead of .Parse(). We cannot trust the users...

Also, if your input might be a real number then culture is an isse, e.g. 3.4 or 3,4.

answered Jun 19, 2017 at 7:53

Patrick Ribbing

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