isdigit to work with negative numbers

[george8000]

Ok well i know that isdigit in my code is seeing the negatives as a character and so i made my program give an error message. But i need negative numbers to work how could i get this to work with negative numbers.

The code is supposed to add the 3 numbers input into the command line argument including negative numbers.

#include <stdio.h>
#include <stdlib.h> 
#include <ctype.h>
#include <string.h>
 
 
int main(int argc, char *argv[]){
 
   int add=0;
   int i;
   int sum;
 
   if(argc == 4){
      for(i=1; i<argc; i++){
         if(isdigit(*argv[i]) == 0){
            fprintf(stderr, "%s: found non-numerical arg\n",argv[0]);
            return EXIT_FAILURE;
         } else if(isdigit(*argv[i]) !=0){
            sscanf(argv[i],"%d",&sum);
            add = add +sum;
         } 
      }
      printf("%d\n",add);
   } else{
      fprintf(stderr,"incorrect number of args\n");
   }
   return EXIT_SUCCESS;
}

[Rabbit]

Use an or to check for the negative sign when looking at the first character.

[george8000]

Omg lol so simple, thanks heaps. I did however have to swap my if statements around aswell because the or statement for the - sign is true in both cases and tends to just output the first if statement