Your program will first prompt the user to enter a single dna sequence, which it should validate for legality (i. e., only the four valid bases) — you might do this validation by writing a function that takes a string as a parameter and returns a boolean. re-prompt the user if the input was invalid. once you have a valid input, compute the following statistics (each should be implemented as a separate function, called from

count the number of occurrences of "c".

determine the fraction of cytosine and guanine nucleotides. for example, if half of the nucleotides in the sequence are either "c" or "g", the fraction should be 0.5.