% cat atoi.C

#include <String.h>
#include <stdlib.h>

/* Demonstration of atoi (and automatic type casting)

   Written by: Charles Severance Sun Feb 19 12:32:07 EST 1995
*/

main() {

  String str;
  int i;

  while (! cin.eof() ) {
    cout << "Enter something ";
    cin >> str;
    if ( str == "end" ) break;
    i = atoi(str);
    cout << "atoi(" << str << ") returns " << i << endl;
  }

} 
% g++  atoi.C
% a.out 
Enter something 123
atoi(123) returns 123
Enter something -123
atoi(-123) returns -123
Enter something ralph
atoi(ralph) returns 0
Enter something amy
atoi(amy) returns 0
Enter something 0
atoi(0) returns 0
Enter something end
%