txtLoadMass.Text = (int.Parse(txtGross.Text) - int.Parse(txtTarre.Text)).ToString(); code example

Example 1: string to int c#

int x = Int32.Parse("1234");

Example 2: c# convert string to int

int number;
bool result = int.TryParse("12345", out number);
if(result)
                {
                    // Do whatever.
                }
                else
                {
                    // Failed to parse.
                }