Vigenere.c has some problem in accepting alpabetic as a key

Question

when i give an input of ./vigenere abc it doesn't accept and its printing key must be alphabetic.where have i gone wrong.would anyone explain in brief? and how do i correct it? Please help me out.!

 int main(int argc,string argv[])
 {
  if(argc!=2)
   {
    printf("Usage: ./vigenere k\n");
    return 1;
   }
 for(int i=0,l=strlen(argv[1]);i<l;i++)
 {
  string k=argv[i];
  if(!isalpha(k[i]))
   {
    printf("key must me alphabetical\n");
    return 1;
   }}

[EDIT: unrelated code removed.]

Answer 1

Look at where and how k is declared. During each pass through the for loop, k is declared as starting at argv[i]. That means that on the first pass, k=argv[0], the name of the program. This sneaks past, as does the next pass. On the third pass, string k=argv[2], which doesn't exist, so it fails.

Remember, argv[x] is a string in the argv array. argv[1][x] are letters in the second string in the array, i.e., if the string is "abc" then argv[1][1] == 'b'

k should be declared once, before the loop starts, and then the loop can step through the string.

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