how to add two string value and display it in string value

Try this :

string tot = (int.Parse(tot) + int.Parse(amtusd)).ToString();

One of the ways:

 // Sample addition of string and a number
string concatenatedString = String.Empty;
string someString1 = "StringABC";
string someString2 = "1234";
int someNumber = 678;
concatenatedString =  someString1 + someString2 + someNumber.ToString();

Now, couple of strings if concatenated is fine like this. If you want to concatenate lots of them, then you should use StringBuilder[^].

UPDATE:
If numbers (in string format) to be added and then again converted to string then:
for string to numbers, read: Int.Parse or Convert.ToInt32
for converting numbers to string, read: ToString() method.

Hi,

Firstly, are you wanting to add int together, or double? or decimal?

I will base it on Double, (that way it will kinda do both)

public static double? ConvertToDouble(string p_dblToConvert)
      {
          try
          {
              return double.Parse(p_dblToConvert.Trim());
          }
          catch (Exception)
          {
              return null;
          }
      }
private static string AdditAndReturnIt(string p_no1, string p_no2)
      {
          double? no1conv = ConvertToDouble(p_no1);
          double? no2conv = ConvertToDouble(p_no2);
          if ((no1conv != null) & (no2conv != null))
          {
              return (no1conv + no2conv).ToString();
          }
          return "";
      }

Using it, I just dragged 3 textboxes and a button to a form, and on button click event...

private void button1_Click(object sender, EventArgs e)
       {
           string no1 = textBox1.Text;
           string no2 = textBox2.Text;
           textBox3.Text = AdditAndReturnIt(no1, no2);
       }

Hope this is what you were thinking

Good luck