How to fix this problem in Vigenere?

Question

I am getting issues in output for the text where we have a space or any other character except alphabets.Key characters are not going with correct s[i], for example:

if i have a text meet me at the park and key word Bacon then the character after space in the text gets with b rather than n.I am not able to fix it,

Plz help

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

int main (int argc,string argv[])
{
    if ( argc!=2)
    {
        printf("./vigenere string\n");
        return 1;
    }
    int n=strlen(argv[1]);
    string s=GetString();

    for (int i=0,l=strlen(s);i<l;i++)  
    {  
        if(isalpha(s[i])&& isalpha(argv[1][i%n]))
        {
            if (isupper(argv[1][i%n]) && isupper(s[i]))
            {
                char d=argv[1][i%n];
                int t=(int)d;
                t=t-65;
                int u=(int)s[i];
                u=u-65;
                int v=(t+u)%26+65;
                printf("%c",(char)v); 
            }

            if (islower(argv[1][i%n]) && islower(s[i]))
            {
                char d=argv[1][i%n];
                int t=(int)d;
                t=t-97;
                int u=(int)s[i];
                u=u-97;
                int v=(t+u)%26+97;
                printf("%c",(char)v);

            }

           if( isupper(argv[1][i%n]) &&islower(s[i]))
           {
               char d=argv[1][i%n];
               int t=(int)d;
               t=t-65;
               int u=(int)s[i];
               u=u-97;
               int v=(t+u)%26+97;
               printf("%c",(char)v);
           }

           if( islower(argv[1][i%n]) &&isupper(s[i]))
           {
               char d=argv[1][i%n];
               int t=(int)d;
               t=t-97;
               int u=(int)s[i];
               u=u-65;
               int v=(t+u)%26+65;
               printf("%c",(char)v);
           }
      }    
      else  
      {  
          printf("%c",s[i]);
      }
   }
}

Answer 1

When there is a space or character other than alphabets, i gets still incremented. Since you are using i for both strings to shift. bacon also gets shifted to next element. I would suggest to use another variable instead of i for bacon.

for example, declare a variable before for Loop. lets say i

 int j = 0; 

and use j in all places in

 argv[1][j%n]

instead of i;

In that case whenever you enter into one of the if's, Increment j.

for example:

 if (isupper(argv[1][j%n]) && isupper(s[i]))
        {
            char d=argv[1][j%n];
            int t=(int)d;
            t=t-65;
            int u=(int)s[i];
            u=u-65;
            int v=(t+u)%26+65;
            printf("%c",(char)v); 

            // Here increment j
            j++;
        }

You have to replace other i wiht j as well.

good luck.

Answer 2

first, your for loop is not well written out, for example I see no condition. hopefully it's a code Post problem. fix it first. then your parenthesis are not completely matched, like you didn't close the main and the else.