arrays - Problem with converting string to integer

Question

(I am very new to both coding and C.)

I want to check if the nr one string in "string argv" is one or more decimals and if it is convert it to an integer. I think I may need to iterate over the string but so far this code is not working. It says segmentation fault.

This is my code:

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

int main (int argc, string argv [])
{

    //check command line
    if (argc == 2)
    {
        printf("success");
    }
    else
    {
        printf("Usage: ./caesar key.");
    }

    //validate number
    if (isdigit (argv[1]))
    {
        int x = atoi(argv[1]);
        printf("I is now %i
", x);
        return 0;
    }

    if (isalpha(argv[1]))
     {
        printf("Usage: ./caesar key
");
        return 1;
    }
}

question from:https://stackoverflow.com/questions/65906819/problem-with-converting-string-to-integer

Answer 1

main function takes (int argc, char *argv[]) parameters. argv is a pointer to pointer and argv[1] is a pointer to a char array too. You should send a character to isdigit and isalpha, not a pointer. You get a segmentation fault because of this probably.