c++

I am puzzled on how to read an input file by line then count the characters a-z (either uppercase or lowercase) and then writing the char and count to an output file. I need to cycle through the input file until the end of file. The formal directions are " the function first reads the paragraph string from the input file stream, then counts the letter frequencies of that paragraph, and store the frequencies in the array. Disregards upper/lower case letters." this function will take in a file stream array and a pointer to an array of integers.