Question

This C program I am making reads a set of chars from the command line and stores them using an array (argv[]) like so

main (int argc, char *argv[])  {
int temp;
     /*prevents no arguments*/
if (argc==1){
    printf("Usage;\t[0 < integers < 9] [operators]\n");
    exit(0);
}
int i;
for (i = 0 ; i<argc; i++){
    temp = argv[i] - '0';
    printf("this is char %d ; %d\n",i, temp);
}
}

But all I get after running it in the command line like so;

    program 2 4 1 - +

is random garbage

    this is char 0 ; -4195956
    this is char 1 ; -4195950
    this is char 2 ; -4195948
    this is char 3 ; -4195946
    this is char 4 ; -4195944
    this is char 5 ; -4195942

Is there something wrong with the way I’m casting temp? Or am I just getting the idea of pointers (in *argv[]) wrong?

Answer 1

char *argv[]

argv is an array of pointers to char. So argv[X] is a pointer to char (for suitable X). So argv[X] - some_integral_value is pointer arithmetic, and returns a pointer (if that subtraction is defined).

To access the first element, you need argv[X][0].

Please note that argv[0] is not the first argument but (usually) the program name. Arguments start at argv[1].