Command line argument example 02

CLA02.cpp

// Command line argument example #02

#include <iostream>
using namespace std;

bool isNum(char *st) {
  int i = 0;
  while (st[i] != '\0') {
    if (st[i] < '0' || st[i] > '9')   return false; 
    i++;
  }
  return true;
}

int main ( int argc, char *argv[] )
{
  int N = 0;
  int a = 0;
  if ( argc < 2 ) {
    cout<<"usage: "<< argv[0] <<" <integer>\n";
    exit(1);
  }
  else if (!isNum(argv[1])) {
    cout<<"parameter: "<< argv[1] <<" is not a valid number.\n";
    exit(1);
  }
  N = atoi(argv[1]);
  for (int i=1; i<N; i++) a += i;
  cout << "Sum is " << a << endl;
}