Restriction of decimal points and correct the number to 2 decimal places in DataGrid View

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C#

.NET4

I created Codes for Validating Textbox Correct to 2 decimal Places using the code given below.

private void txtAge_KeyPress(object sender, KeyPressEventArgs e)
        {
            string str = txtAge.Text;                               //  User Control
            int len = str.Length;
            int index = 0;
            int dcml = 2;                                           // 2 indeicates the Deccimal Points Needed   (User Defined)
            if (str.Contains('.'))
            {
                index = str.IndexOf('.');
                index = len - index;
            }
            if (Char.IsControl(e.KeyChar) == false)
            {
                if (((Char.IsDigit(e.KeyChar)) && (index <= dcml)) || ((e.KeyChar == '.') && (!(str.Contains('.')))))
                {
                }
                else
                {
                    e.Handled = true;
                }
            }
        }

but I cannot use this code to Correct the Text Validation in Data Grid View, string str is not taking the value from datagridview cell. it gets only the null values. but It accepts only digits and decimal points. I can enter any number of decimal points and any numbers after decimal point. How can i change this, restricting the value to 2 decimal places and allow only one decimal point.