** Start of listing of h4int.cc **
/* Stub: How to build h4int-c++.cgi ?
   Answer: fake header below compiles whole module right in, so trivial build:
g++ h4int.cc
mv h4int-c++.cgi ~/Trash
mv a.out h4int-c++.cgi
*/

#include <iostream>
#include <string>
#include <sstream>
using std::cout;
#include "CGI-cc.h" // Warning, that's not a header, it's the whole source!!

CGI c; // Contains all the CGI info. See CGI-cc.h for access methods.
char* br = "<br />";
char* nl = "\n";

#define maxch 10
enum errcode {good=0, nonum=-1, garbfnum=-2, signxnum=-3, garafnum=-4};

/* Given a string (nul-term), find start of number, + - or digit,
   pass back index by side-effect, and return 0 if OK or negative errcode:
   nonum = end without number, garbfnum = garbage before number */
enum errcode strchkint1(string str, int* pix) {
  (*pix)=0;
  while (1) {
    if (str.size() <= *pix) {
      //cout << "At ix=" << *pix << "endOfString before startOfNumber.\n";
      return(nonum);
    }
    char ch = str.at(*pix);
    if ('\n' == ch) {
      //cout << "At ix=" << *pix << ", ch='" << ch << "', eol before start of number.\n";
      return(nonum);
    }
    if (('+' == ch) || ('-' == ch)) {
      //cout << "At ix=" << *pix << ", ch='" << ch << "', found sign.\n";
      return(good);
    }
    if (('0' <= ch) && ('9' >= ch)) {
      //cout << "At ix=" << *pix << ", ch='" << ch << "', found digit.\n";
      return(good);
    }
    if (' ' == ch) {
      //cout << "At ix=" << *pix << ", ch='" << ch << "', skip white.\n";
      (*pix)++;
    }
    else {
      //cout << "At ix=" << *pix << ", ch='" << ch << "', garbage, aborting.\n";
      return(garbfnum);
    }
  }
}

/* Given a string (nul-term), and index where first digit or sign found,
   skip just the sign if that's what was found, update index,
   make sure a digit is immediately after the sign,
   return 0 if ok else error code: signxnum = sign without number */
enum errcode strchkint2(string str, int* pix) {
  char ch = str.at(*pix);
  if (('+' == ch) || ('-' == ch)) {
    //cout << "At ix=" << *pix << ", ch='" << ch << "', it was sign.\n";
    (*pix)++;
  }
  if (str.size() <= *pix) {
    //cout << "End of string immediately after sign!\n";
    return(signxnum);
  }
  ch = str.at(*pix);
  if (('0' <= ch) && ('9' >= ch)) {
    //cout << "At ix=" << *pix << ", ch='" << ch << "', it was digit.\n";
    return(good);
    }
  //cout << "No digit after sign!\n";
  return(signxnum);
}

/* Given a string (nul-term), and index where first digit found,
   scan to end of digits, update index, return code always 0 (OK). */
enum errcode strchkint3(string str, int* pix) {
  while (1) {
    if (str.size() <= *pix) {
      //cout << "At ix=" << *pix << ", end-of-string after digits.\n";
      return(good);
    }
    char ch = str.at(*pix);
    if (('0' <= ch) && ('9' >= ch)) {
      //cout << "At ix=" << *pix << ", ch='" << ch << "', saw digit.\n";
      (*pix)++;
    }
    else {
      //cout << "At ix=" << *pix << ", ch='" << ch << "', no more digit.\n";
      return(good);
    }
  }
  }

/* Given a string (nul-term), and index where digits ended,
   scan to very end making sure no junk, return code:
   garafnum = garbage after number */
enum errcode strchkint4(string str, int* pix) {
  while (1) {
    if (str.size() <= *pix) {
      //cout << "At ix=" << *pix << ", end-of-string after digits.\n";
      return(good);
    }
    char ch = str.at(*pix);
    if ('\n' == ch) {
      //cout << "At ix=" << *pix << ", ch='" << ch << "', eol reached.\n";
      return(good);
    }
    else if (' ' == ch) {
      //cout << "At ix=" << *pix << ", ch='" << ch << "', skip white.\n";
      (*pix)++;
    }
    else {
      //cout << "At ix=" << *pix << ", ch='" << ch << "', junk.\n";
      return(garafnum);
    }
  }
}

/* Given a string (nul-term), and integer where to put the final index,
   check if string consists exactly of representation
   of an integer (except for surrounding whitespace which are ignored).
   Return 0 (true) if it's all correct, an error code otherwise.
   Index is updated to point to EOL or NUL at end of string if all OK,
   else index points to first problem spot. */
enum errcode strchkint(string str, int* pix) {
  enum errcode scanres;
  if (0 != (scanres = strchkint1(str,pix))) {
    //cout << "scanres#1=" << scanres << ", ix=" << *pix << ", aborting.\n";
  }
  else if (0 != (scanres = strchkint2(str,pix))) {
    //cout << "scanres#2=" << scanres << ", ix=" << *pix << ", aborting.\n";
  }
  else if (0 != (scanres = strchkint3(str,pix))) {
    //cout << "scanres#3=" << scanres << ", ix=" << *pix << ", aborting.\n";
  }
  else if (0 != (scanres = strchkint4(str,pix))) {
    //cout << "scanres#4=" << scanres << ", ix=" << *pix << ", aborting.\n";
  }
  else {
    //cout << "scanres#4=" << scanres << ", ix=" << *pix << ", stub.\n";
  }
  return(scanres);
}

/* Given bad results from strchkint, i.e. index where scan stopped and error
   code which is nonzero, describe problem to user. */
void tellproblem(string str, int ix, enum errcode erc) {
  switch (erc)
    {
    case nonum: cout << "Not a single digit anywhere.\n"; break;
    case garbfnum:
      if (0==ix) { cout << "Right at the very start: "; }
      else {
	cout << "Everything was fine for " << ix << " characters, ";
	cout << "just whitespace, but then: ";
      }
      cout << "a garbage character '" << str.at(ix) << "'.\n"; break;
    case signxnum:
      if (1==ix) { cout << "Right at the very start: "; }
      else {
	cout << "Everything was fine for " << ix << " characters, ";
	cout << "just whitespace, but then: ";
      }
      cout << "sign '" << str.at(ix-1) << "' followed by ";
      if (str.size() <= ix) { cout << "end of string already.\n"; }
      else { cout << "non-number '" << str[ix] << "'.\n"; }
      break;
    case garafnum: cout << "Everything was fine, optional whitespace and ";
      cout << "sign, and good number, but then garbage character '" <<
	str[ix] << "'.\n"; break;
    default: cout << "(Stub, other case #" << erc << ")\n";
    }
}

void keygetchecktell(char* key) {
  char *fn;
  if ((fn = c.copy_value(key)) == NULL) {
    cout << "Your form doesn't contain any [" << key << "] field." << br << nl;
    return;
  } else {
    cout << "For key [" << key << "] the value is [" << fn << "]."
         << br << nl;
  }
  int ix;
  enum errcode scanres = strchkint(fn,&ix);
  if (0 != scanres) tellproblem(fn, ix, scanres);
  else cout << "Hey, you got it correct, a number in that form-field!";
  cout << br << nl;  
  }

main() {
  char* qs = getenv("QUERY_STRING");
  c.start_html("Robert Maas CalRobert642@Yahoo.com",
	       "Test CGI Page- written using C++ Include file",
	       "white");
  std::cout << "The query string is: [" << qs << "]" << br << nl;

  char *key; /* Will point to various literals */
  char* fn;
  int ix;
  enum errcode scanres;

  cout << "**WARNING** Untested new stuff ..." << br << nl;

  keygetchecktell("num1");
  keygetchecktell("num2");
  keygetchecktell("num3");
  keygetchecktell("num4");
  keygetchecktell("num5");
  keygetchecktell("num6");
  keygetchecktell("num7");
  keygetchecktell("num8");

  /* while (1) { cout << "Type a number:"; string line; std::getline(cin, line); cout << "You typed the string [" << line << "]\n"; enum errcode chkres; int ix;
     chkres = strchkint(line, &ix); cout << "Toplevel result: chkres=" << chkres << " ix=" << ix << "\n"; if (0 != chkres) tellproblem(line, ix, chkres);
     if (chkres==0) { int n; istringstream(line) >> n; cout << "The number was [" << n << "]\n"; } else cout << "Skipping the number parse this time around.\n"; }
  */
}
** End of listing of h4int.cc **

Here is the directory entry for that source file:
-rw-------  1 rem  user  7619 Feb 10  2007 h4int.cc
   ^ Note user execute permission *not* needed for source files.

That gets compiled to a.out, but then renamed to something.cgi
so that it will be usable by remote users via CGI:
-rwx------  1 rem  user  39936 Feb 10  2007 h4int-c++.cgi
   ^ Note user execute permission needed for all CGI programs.
(because compiled-C++ is native machine code running directly on machine)