How do I write a program counted letters in C#?

[Mer Ste]

Write a program that creates a probabilistic model for a text file with counted occurrences of specific letters.
And it must display it in the table how many individual characters (in ASCII code) are in the text read from the file.
and the probability calculated using:
P = number of occurrences / all characters

What I have tried:

var plik = File.ReadAllLines("example.txt");
       var liczba = 'z' - 'a' + 1;
       
       var liczniki = Enumerable.Repeat(0, liczba).ToList();
       
       foreach (var słowo in plik) {
           foreach (var znak in słowo) {
               
               if (znak >= 'a' && znak <= 'z') {
                   liczniki[znak - 'a'] += 1;
               }    
           }

[Campbell Ritchie]

Does that code work? Have you tested it? I have only had a very quick look at it, and I hardly know any C#, but it looks all right.
How are you calculating the total?
Are you getting 0 for all your “P”s?

[Piet Souris]

If you are familiar with Dictionaries,  then it is easy to make a frequency table. The total number is the sum of the values, and the probabilities are easy to calculate.

[Campbell Ritchie]

Piet Souris wrote:. . . Dictionaries . . . a frequency table. . . .

And there is an example very similar to that in the Java™ Tutorials.