Thread: CS50 Caesar - Checking a string for digits

I'm currently going nuts with a problem called Caesar. Essentially, you need to build a program that encrypts text that the user enters (so, for example - if you entered the number 1 and the plaintext 'Hi' the code that would come back would read 'Ij' as the program would have encrypted the plaintext message by moving the numbers forward by 1).


I have been trying to write the program step by step - it's really easy to find 'complete' versions of the code online but I want to work out how to do each stage. The walkthrough says that you should try and build the program in the following stages:

1. Write pseudocode
2. Count command-line arguments
3. Access the key
4. Validate the key
5. Peek under the hood (which is when you insert the 'formula' to encode the text)

I'm stuck on section 4 - which is when you have to check that the value that the user has entered (in my example above the value was 1) and check it is a digit. As things stand, my program is simply checking whether I have one 'argument' but is not checking whether that argument is a digit, so - if the user typed:


./caesar 20 (This should work and does, it has one argument, and both '2' and '0' are digits)

My program would respond with:

Success
20

If the user typed:
./ caesar 20x (This should fail but doesn't. It has only one argument but one character in the argument 'x' is not a digit)
My program would respond with:

Success
20x

The issue seems to be that my program should be looking at each separate character that the user types in their argument. To do this I think I need to run a loop that iterates through each character in the string (which I think I have done). However, something clearly isn't right and I'm struggling! Any help or advice very much appreciated.

Code:

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


int main(int argc, string argv[])
{
    if (argc != 2)
    {
        printf ("Usage: ./caesar key\n");
    }


    else if (argc == 2)
    {
        int Key = atoi(argv[1]);
        bool isKeyValid = true;
        int len = strlen(argv [1]);


        for (int i = 0; i < len; i++)
        {
            if (isdigit(argv[1][i]) == false)
            {
                isKeyValid = false;
                printf ("Usage: ./caesar key\n");
                i = len;
            }
            if (isKeyValid == true)
            {
                printf ("Success\n");
                printf ("%s\n", argv[1]);
                i = len;
            }
        }
    }
}

I think that your last point - pulling the if (isKeyValid == true) section out of the loop has fixed the problem! Thank you!

Any idea why this worked???