Command line arguments

Another method to get user inout is through the use of command-line arguments when running a program:

  my_program 34 66 dallas

where the arguments 34, 66, and dallas are captured and subsequently used in your program. How this can be done is illustrated in the following program:

#include <stdio.h>

int main(int argc, char *argv[]) {
  int input;

  if (argc != 2) {
    printf("Usage: %s number\n", argv[0]);
    exit(1);
  }
  input = atoi(argv[1]);
  printf("You entered an integer %d.\n", input);
  return 0;
}

Here,

• argc is an integer which will be set equal to the number of arguments used (the name of the program counts as one argument).
• argv is an array of strings containing the command-line arguments used, with the name of the program appearing as the first element (argv[0]).

It is important to realize that the arguments will be captured as strings (arrays of characters); the functions atoi and atof can be used to convert a string to, respectively, an integer and a double.