Vigenère cipher in C, how to shift keyword only on alpha chars

Question

I'm trying to make a Vigenère encryption code for my problem set of the week and I'm almost done. I have a little problem, I can't make the keyword char shift only on alphabetical chars this is my code and I can't track the problem.

GetString() is implemented by library (it's like scanf) & string typedef also

int main(int argc, string argv[])
{
    string keyWord;      
    if( argc != 2  )
    {
        printf("Wrong Argument");
        return 1;            
    }
    else
    {
        keyWord = argv[1]; 

        //check if argument is 
        //only alphabetical characters
        for(int i = 0; i < strlen(keyWord); i++)     
        {
            char c = keyWord[i];
            if( !isalpha(c) )
            {
                printf("Your Keyword Must Contain Only alphabetical characters\n");
                return 1;
            }                                    
        }
    }

    string plainText = GetString();       

    for(int i = 0,j = 0; i < strlen(plainText); i++,j++) 
    {                        
        if(j >= strlen(keyWord))
            j = 0;                

        char c = plainText[i];
        int keyWordWrapper;
        char keyC;                                  

        if(isalpha(c))
            {                     
                keyWordWrapper = j % strlen(keyWord);
                keyC = keyWord[keyWordWrapper];
                int key;
                tolower(c);

                if(islower(keyC))
                 key = keyC - 'a';

                if(isupper(keyC))
                 key = keyC - 'A';                                         
                c = (c - 'a'  + key) % 26 + 'a'; 
            } 
        printf("%c",c);                      
    }

printf("\n");
return 0;
}

Answer 1

you may do the following

    //to skip the spaces
    if(c==32)
      {
         j--;
         continue;         
      }

    char c = plainText[i];
    int keyWordWrapper;
    char keyC;       
    if(isalpha(c))
        {                     
            keyWordWrapper = j % strlen(keyWord);
            keyC = keyWord[keyWordWrapper];
            int key;
            tolower(c);

            if(islower(keyC))
            {
               key = keyC - 'a';
               c = (c - 'a'  + key) % 26 + 'a'; 
            }
            if(isupper(keyC))
            {
              key = keyC - 'A';                                         
              c = (c - 'A'  + key) % 26 + 'A'; 
            }
         }