Why is my Vigenere cypher not processing my keyword correctly?

Question

I have included the part of my cypher responsilble for converting a command line keyword into an array of integers that will indicate by how much each character in a phrase should be shifted in encryption. Ideally, if I enter 'a' as the keyword and 'a' as the phrase to be encrypted, the resulting encryption should be 'b'. As of now though, I get 'K'.

I have included a printf check to see how much the keyword is shifting the phrase, which for the above circumstances is a shift of -48. It should be a shift of 1.

Can anyone tell me how I messed up? I've been trying to figure this out for quite a while.

//prompt the user for a non-neg integer 'k' which is to be used as
//an arg

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

int main (int argc, char *argv[])
{
    if (argc!=2)                //fail if 0 or more than one key
    {
        printf ("PROVIDE JUST ONE COMMAND LINE ARGUMENT\n");
        return 1;
    }

    int keylength=strlen(argv[1]);   // get length of keyword

    int newkey[keylength];
    //deal with upper and lower case chars in keyword first
    for (int j=0; j<keylength; j++) //iterate through each char in key
    {
        if (islower(argv[1][j]))   //if key char is lower case...
        {
            int x = (argv[1][j])-'0';
            int y = x-97;
            newkey[j]= y;  
        }
        if (isupper(argv[1][j]))   //if key char is upper case...
        {
            int x = (argv[1][j])-'0';
            int y = x-65;
            newkey[j]=y;
        }
    }
    printf ("%i\n", newkey[0]);

Answer 1

int x = (argv[1][j])-'0'; looks like your problem. You are subtracting the ascii value of the 0 symbol from the character in argv[1][j]. In effect, you have done int x = (argv[1][j])-48; I don't understand why you are subtracting either 0 or the ascii value of 0 here.

Instead of those 3 lines of code, you could consolidate them into one line and eliminate the intermediate variables.

    newkey[j] = (argv[1][j])-'a';

Why not keep it simple?

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