Write a program that will read a line of text and output a list of all the letters that occur in the text together with the number of times each letter occurs in the line. end the line with a period that serves as a sentinel value. the letter should be listed in the following order: the most frequently occurring letter, the next most frequently occurring letter, and so forth. use an array with a struct type as its base type so that each array element can hold both a letter and an integer. you may assume that the input uses all lowercase letters.