How to write own isnumber() function?

Question

I\'m new to C and I\'m thinking how to write this function myself. I take a parameter from command line, so it is stored in argv array and I want to decide whether it is or

Answer 1

How about trying like this:

#include 

if(isdigit(input))
{
  return true;
}
else
{
  return false;
}

OR more simple as H2CO3 commented:

 #define isnumber isdigit

OR

#include 
#include 
#include 
int main () {

  //some code
  theChar = atoi(string[i]);
  if (isdigit(theChar)) {
    return true;
  }
  return 0;
}