用新的字符串替换字符串的每个字符

Question

The c# program I'm developing checks the first character of user input and if it starts with . (dot) I want to replace each character of user input with pacified character string while the user is writing, but I'm getting the error

Index out of bounds exception

My code:

if (textBox1.Text.StartWith(".")) {
    string MyText = "Hello World";
    int x = 0;
    string NewText;
    while (x <= MyText.Length) {
        NewText = textBox1.Text.Replace(textBox1.Text[x], MyText[x]);
        TextBox1.Text = NewText;
        x++;
    }
}

Answer 1

You're overrunning the bounds of the string, replace:

while (x <= MyText.Length) {

with

while (x < MyText.Length) {

Answer 2

while(x < MyText.Length)

or

while(x <= MyText.Length - 1)

If array has length = x, its last index is x-1, because array starts from 0 index

Answer 3

If I understand you right (there're no samples in question), I suggest using Linq which is straitforward; try using modular arimethics - index % MyText.Length to avoid index problems

string source = ".My Secret Message for Test";
string MyText = "Hello World";

// If user input starts with dot
if (source.StartsWith("."))
  source = string.Concat(source
    .Select((c, index) => MyText[index % MyText.Length])); 

TextBox1.Text = source;

Outcome:

   Hello WorldHello WorldHello

Answer 4

First of all as @Daniell89 said:

use

while(x < MyText.Length)

Secondly: You use x as an index not only for MyText but for textBox1.Text too. So you need to check that it is long enough.

you can do something like this:

while (x < Math.Min(MyText.Length, textBox1.Text.Length)
{
    NewText = textBox1.Text.Replace(textBox1.Text[x], MyText[x]);
    TextBox1.Text = NewText;
    x++;
}

But I think it would be better to use for statement here.