text - Assembly, how to read something from a txt? -

i need read phrase , how many times appears each letter, example:

"hello sir"   h=1, e=1 , l=2, o=0, s=, i=1, r=1  

but dont know how take text txt , use on assembly code.

        using (var sr = new streamreader(@"c:\test.txt"))         {             var str = sr.readtoend();              var charlist = str.distinct().tolist();              foreach (var chr in charlist)             {                 var count = str.count(x => x == chr);                 console.writeline(string.format("{0} : {1}", chr, count));             }         }