Vigenere Cipher

#include <cs50.h>
#include <stdio.h>
#include <string.h>
#include <ctype.h>

void getCipherVaried(string text, string shifts);
int getCaseValue(int originalChar);

int main (int argc, string argv[])
{
    if (argc != 2) //check for two arguments
    {
        printf("please enter two arguments (./vignere ABC)\n");
        return 1;
    }
    string shifts = argv[1];//get the shift arguments
    for (int i = 0; i < strlen(shifts); i++) //make sure each character in the shifts is in the alphabet
    {
        if (!isalpha(shifts[i]))
        {
            printf("please only enter letters!!!!! >:(\n");
            return 1;
        }
    }
    printf("plaintext: "); //ask and store plain text
    string text = get_string();
    getCipherVaried(text,
                    shifts); //send plaintext and shifts to GetCipherVaried, which modifies the text into cyphertext based off the shifts
    printf("ciphertext:%s\n", text ); //print ciphertext
    return 0;

}

void getCipherVaried(string text, string shifts)
{
    int length = strlen(text); //store the length of the text
    int counter = 0; //counter for changing shifts
    int shiftLength = strlen(shifts); //store the length of the shifts
    for (int i = 0; i < length; i++) //iterate over each character of the text
    {
        if (text[i] != ' '
            &&  isalpha(text[i])) //don't do anything if the current character is a char or not alpha
        {
            if (counter > shiftLength - 1) //reset the counter if outsie shifts length
            {
                counter = 0;
            }
            int shift = (int)(shifts[counter]);//get the current shift at the counter location
            shift -= getCaseValue(shift); //get the 0 base value of shift
            int originalChar = (int) text[i]; //get the char, and conver to decimal
            int fromZero = originalChar - getCaseValue(originalChar);
            fromZero = (fromZero + shift) % 26; //add shift to fromZero, then % 26
            text[i] = (char) (getCaseValue(originalChar) +
                              fromZero); //add fromZero to caseValue and return to char, and replace the former value of text
            counter++;
        }
    }
}


int getCaseValue(int
                 originalChar)//get the original char value and return it's case value (97 for lowercase, 65 capital)
{
    int caseValue = 0;
    if (originalChar >= 97)
    {
        caseValue = 97;
    }
    else if (originalChar >= 65)
    {
        caseValue =  65;
    }
    return caseValue;
}




/*$ ./vigenere ABC
plaintext:  HELLO
ciphertext: HFNLP*/