Question

I’m facing unexpected problem in my Caesar’c cipher. Caesar is when you encrypt text by shifting every letter by n numbers. So if it is 1, abc will be bcd. I work on the program that does that in C, but it works strange for some characters, regular letters, although it should be correct. Here is the problem syntax:

    for (int i = 0; i < strlen(text); i++)
{   
    if (text[i] != ' ')
    {
       // printf("\n%i\n", key);

        text[i] = text[i] + key;


        if (text[i] > 122)
        {
            text[i] = text[i] + 97 - 122; 
        }


    }
}

I wrap around by doing that math in the end.
Can you please help me whats wrong with it?

EDIT: This code is fine, problem is with handling of command line parameters.

Answer 1

Use 96 in place of 97 problem solved

so when you wrap around then actually increase by 1 extra value
think of this;

    ------------------------------------------
    a  |  b |  c |  d  | . . . x  |  y  |  z  |
    --------------------------------------------
    97 | 98 | 99 | 100 | . . .120 | 121 | 122 |
    -------------------------------------------

Try using ‘a’ , ‘b’ , .. .. .. ,’z’ like this rather their actual values

using ' 'single quote inside char gives you integral value i.e. ASCII value

here is the code :

char c;
for (int i = 0; i < strlen(text); i++)
{   
    if (text[i] != ' ')
    {
       // printf("\n%i\n", key);

        c=text[i];    
        text[i] = text[i] + key;

        if(c >='a' && c <='z' && text[i] >'z')
            text[i] = text[i] + 'a' -1 - 'z' ; 

        if(c >='A' && c <= 'Z' && text[i] > 'Z')
            text[i] = text[i] + 'A' -1 - 'Z' ; 

    }
}