rohan rohan - 4 months ago 71
C Question

What's wrong with this vigenere cs50 code?

It just isn't working. Can you point out what's wrong? When I run it I get:

jharvard@appliance (~/Dropbox/pset2): ./vigenere bacon
Meet me at the park
ARTU [R \T aW` ^NaL


Which is clearly wrong. I've spent countless hours on this. here is code:

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

int main(int argc,string argv[])
{
if(argc!=2)
{
printf("Usage: /home/cs50/pset2/caesar <key>\n");
return 1;
}
else
{
char *k = argv[1];
string p = GetString();
int klen = strlen(k);

for(int i=0; i<klen;i++)
{
if(isupper(k[i]))
{
k[i] = k[i]-65;
}
else if (islower(k[i]))
{
k[i] = k[i]-97;
}

}

for(int i=0, n=strlen(p); i<n;i++)
{

if(isupper(p[i]))
{
printf("%c", (((p[i]-65)+(k[i%klen]-65))%26)+65);
}
else if (islower(p[i]))
{
printf("%c", (((p[i]-97)+(k[i%klen])-97)%26)+97);
}

else
{
printf("%c", p[i]);
}

}
printf("\n");

}
}

Answer

As noted in comments, the code for the loop over p should be :

EDIT per comment : code is adapted to skip non alpha charactes

int j = 0
for(int i=0, n=strlen(p); i<n;i++)
{

        if(isupper(p[i]))
        {
            printf("%c", (((p[i]-65)+(k[j%klen]))%26)+65);
            j += 1
        }
        else if (islower(p[i]))
        {
            printf("%c", (((p[i]-97)+(k[j%klen]))%26)+97);
            j += 1
        }

        else
        {
           printf("%c", p[i]);
        }
}

And the output for ./vigenere bacon with Meet me at the park should be :

Negh zf av huf pcfx