C# 错误运算符 * 不能应用于“字符串”和“字符串”类型的操作数

Question

public partial class Form1 : Form
{
    string principal, rate, years;
    public Form1()
    {
        InitializeComponent();
    }
    private void button1_Click(object sender, EventArgs e)
    {
        principal = loantextBox4.Text;
        rate = ratetextBox5.Text;
        years = yearworktextBox2.Text;

        outputlabel5.Text = principal * ((rate * (1 + rate) ^ years) / ((rate + 1) ^ years) - 1))));

What needs to be fixed I keep getting an error saying operator "*" cannot be applied to operands of type 'string' and 'string'.

Answer 1

You cannot apply mathematical operations on a string variable and thus you need an int or double type. I have used int . Secondly When you try to get the TextBox data in the int variable it would not be possible because TextBox.Text would return a string. Now You can convert the TextBox.Text to a int using Convert.ToInt32 . If you try to put the values of the Textbox to int variable without conversion, it will give you an error stating

Cannot implicitly convert type 'string' to 'int'

and it would not even compile the program.

Whereas letz say if the user input in not a number and it we try to Convert it. For example the user input is "Mohit" and when it tries to convert the Convert.ToInt32("Mohit"); it will throw an exception. stating

An unhandled exception of type 'System.FormatException' occurred in mscorlib.dll

You can avoid getting exception or to handle the wrongly input from the user you can use Try and Catch Block

Hope this code will give you the idea

public partial class Form1 : Form
{
    int principal, rate, years;
    public Form1()
    {
        InitializeComponent();
    }
    private void button1_Click(object sender, EventArgs e)
    {
        principal = Convert.ToInt32(loantextBox4.Text);
        rate = Convert.ToInt32(ratetextBox5.Text);
        years = Convert.ToInt32(yearworktextBox2.Text);

        outputlabel5.Text = (principal * ((rate * (1 + rate) ^ years) / ((rate + 1) ^ years) - 1)).ToString();

Answer 2

You can't multiply strings. You can , however, multiply numbers. Convert your numeric strings to numbers. For example:

int years;
if (!int.TryParse(yearworktextBox2.Text, out years))
{
    // string value wasn't numeric, maybe show an error?
    // probably return from here as well, since the logic can't continue
}
// here the "years" value can be used for calculations

Remove the string variables you have, replace them with numeric values ( int , decimal , double , etc. where appropriate) which are populated by parsing the input strings using .TryParse() (and handling errors accordingly), then you can use those values in your calculations.

Answer 3

Because all of your inputs are strings. You can't multiply a string.

What you need to do instead is change them to a number format. Probably just int should be fine.