system(PAUSE);

[joe_bruin]

i've seen several people use system("PAUSE") when they want to delay their programs. i'm not sure who's teaching this method, but it's a bad habit.
by calling system(), you are invoking the default shell. the shell then executes the commandline given to it ("PAUSE", in this case). that is, it runs the 'pause.exe' program. so, now your simple c program is relying on two external programs for a stupid thing like pressing a single key. what if someone deleted or renamed 'pause.exe'? what if someone tried to compile your program on unix, or a mac? it wouldn't work. you'd get an annoying shell message and no pause. besides, why have the overhead of launching 2 programs, when you can accomplish the same thing in c?

so, for those of you who are starting out, here is an implementation in c for use in your programs that does essentially the same thing.

#ifndef WIN32
 #include <unistd.h>
#endif

#ifdef __cplusplus
 #include <iostream>
  #ifndef WIN32
   #include <stdio.h>
  #endif
 using namespace std;
#else
 #include <stdio.h>
#endif

#define WAIT_MSG "press enter to continue..."

/*
 note that the function "pause" already exists in <unistd.h>
 so i chose user_wait() for it.
*/
void user_wait()
{
  int c;

#ifdef __cplusplus
  cout << WAIT_MSG << endl;
#else
  printf("%s\n", WAIT_MSG);
#endif
  /* eat up characters until a newline or eof */
  do
  {
    c = getchar();
    if(c == EOF) break;
  } while(c != '\n');
}

here is a simple program that uses it

int main(int argc, char *argv[])
{
  printf("hello\n");
  user_wait();
  printf("goodbye\n");
  return 0;
}

the main problem with it is that console io is usually line buffered, so it requires a newline, instead of 'any' key. there are system-specific ways to override this (which is what 'pause.exe' does), but this code should be portable to most systems.

[Valmont]

ADDENDUM: standard C++

The code below occasionally works...

#include <iostream>
int main(int argc, char *argv[])
{
  std::cin.get();
  return 0;
}

...but does not suffice.
In that case some do advice to add

std::cin.sync();

before std::cin.get(); to clear the stream buffer. That might easely not suffice as well. You'll need to add a little more code to make it work after input (e.g. cin>>MyVar). I'll present you the code below wich will work quite effortlessly:

#include <iostream>
#include <string>

//Namespace std to keep this small code readable.
//However, one shouldn't use the standard namespace globally the
//way I do here.
using namespace std;

void reset_istream(istream & is)
{
   char ch;
   // Reset the state.
   is.clear();
   // Remove all characters until we find a newline or EOF.
   ch = is.get();
   while ((ch != '\n')&&(ch != EOF))
      ch = is.get();
   is.clear();
}

void wait_for_enter()
{
   cout << "press <enter> to continue...\n";
   // Reset failstate, just in case.
   cin.clear();
   string line;
   getline( cin, line);
}

int main()
{
   //Your code here;   

   reset_istream(cout);
   wait_for_enter();

   return 0;
}

This should work in most cases. Notice that sometimes you don't need "reset_istream()" at all. You'll find out soon enough so no worries.

- Val -