How to I compare elements of two arrays

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C#

Visual-Studio

C#7.0

Basically i want to be able to compare elements of arrays and identify if any elements are similar.

The code below works only sometimes, when a word has five letters such as "Hello and Hello" it gives out 7, when the word has 4 letters such as well "Hello and hell" it gives out 6, and it gives out 2 when only 2 are similar.

What I have tried:

if(GuessLenght == WordLenght)
            {
                //Check Each Element

                foreach(char Letter in ActualChar)
                {
                    foreach(char letter in GuessChar)
                    {
                        if(Letter == letter)
                        {
                            LetterGuessed++;
                        }
                        else
                        {
                            
                        }
                    }
                }
            }