/* 21.6 -- (Count the occurrences of numbers entered) Write a program that reads an
unspecified number of integers and finds the one that has the most occurrences. The
input ends when the input is 0. For example, if you entered 2 3 40 2 5 4 -3 3 3 2 0,
the number 3 occurred most often. If not one but several numbers have the most
occurrences, all of them should be reported. For example, since 9 and 3 appear
twice in the list 9 30 3 9 3 2 4, both occurrences should be reported.
*/