Why does Parse work and Convert doesn't in C#?

Question

I want to square every digit in str and concatenate it to pow.

I have this simple code:

string str = "1234";
string pow = "";

foreach(char c in str)
{
   pow += Math.Pow(Convert.ToInt32(c), 2);
}

It should return 14916 - instead it returns: 2401250026012704

But if I use int.Parse(c), it returns the correct number.

foreach(char c in str)
{
    int i = int.Parse(c.ToString());
    pow += Math.Pow(i, 2);
}

Why does Parse work and Convert doesn't?

Answer 1

From the documentation of Convert.ToInt32(char):

The ToInt32(Char) method returns a 32-bit signed integer that represents the UTF-16 encoded code unit of the value argument.

Therefore, for example, the char '1' will be converted to the integer value 49, as defined in the UTF-16 encoding: https://asecuritysite.com/coding/asc2.

---

An alternative approach to the int.Parse(c.ToString()) example, would be Char.GetNumericValue:

foreach(char c in str)
{
   pow += Math.Pow(char.GetNumericValue(c), 2);
}

This converts the char to the numeric equivalent of that value.