break a FOR loop with keyboard in C

Question

I have a program that runs through a few steps before it starts a for (;;) loop.

I want to be able to break; this for loop using a keystroke (such a 'e' for exit, for example)

I've tried scanf_s but I don't think I am using them correctly. the loop just doesn't initiate if I try to write scanf_s in.

I'm not very familiar with C programming so I'm struggling a little bit.

Can someone shed some light on this?

extra info:

Operating system is Win 8.1.

Program is a TCP server program. it creates a socket and begins listening. Then it starts accepting client connections in a for loop. then begins another for loop to receive messages from the client.

Edit: using this I have managed to stop the second for loop with s. added the changes to the simplified code (and just bellow).

added:

if (_kbhit()) {
    key = _getch();
    if (key == 's');
    break;
}

here is some simplified code:

#include <winsock2.h>
#include <ws2tcpip.h>
#include <stdio.h>
#include <stdlib.h>

int main(void)
{
    // prelim info goes here
    // like SOCKET 
    // and struct sockaddr_in

    // Initialize Winsock
    WSAStartup();

    // Create socket
    mysocket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);

    // server parameters go here 
    // like sin_addr and sin_port

    bind(mysocket);

    // start listening
    listen(mysocket, SOMAXCONN);

    // begin the damn for loops

    for (;;)
        {

        myclient = accept();

         //second for loop
        for (;;)
        {
            receivedata = recv(myclient);

            printf(<data>)

            if (_kbhit()) {
                key = _getch();
                if (key == 's');
                    break;
            }

        }
    }

    // close socket
    closesocket(mysocket);

   // call WSACleanup
   WSACleanup();

   return 0;
}

thanks to everyone who supplied links and the helpful answers. The issue with the outer loop turned out to be a bit more involved than just breaking it. However, if any future visitors are wondering how to break a loop with a keyboard press, this has been achieved. See the correct answer or my simplified code.

Answer 1

You can try using kbhit and getchar to check keystroke and handle the action accordingly. Check this post: Return pressed key without enter for confirmation

This code breaks the while loop when e is pressed: [Code updated with one more extra while loop]

#include <stdio.h>
#include <conio.h>

int main(){
    int ch = '1';
    while(ch != 'e'){                        //outer while for accepting connection
        printf("waiting for connection\n");  //do something

        while(ch != 'e'){                    //inner while for checking key press
            if(kbhit())                      //if key is pressed
                ch = getch();                //get the char and set ch to 'e'
        }
    }

    return 0;
}

Old Code using break:

#include <stdio.h>
#include <conio.h>
#include <windows.h>
int main(){
    int ch;
    while(1){
        printf("*");
        if(kbhit()){               //if key is pressed
            ch = getch();          //get the char
            if(ch == 'e')          //if pressed key is 'e'
                break;             //break while loop 
        }
    }

    return 0;
}

Answer 2

just enter these lines in for loop. this will exit when user will enter 'e' char.

    if(kbhit()){              
  ch = getch();          
  if(ch == 'e')          
    break;             
    }`

Answer 3

Assuming Microsoft's compiler, the simplest method is to use its conio library. I suggest wrapping the details into a single function, to allow reuse. For example, you may need to test the keyboard before entry to the second loop.

#include <conio.h>

int nonBlockingGetch( void )
{
    int ch = -1 ;
    if( _kbhit() )
    {
        ch = _getch() ;
    }

    return ch ;
}

int main( void )
{
    int ch = -1 ;

    //  Outer loop
    while( ch != 'e' )
    {

        // inner loop
        while( ch != 'e' )
        {
            ch = nonBlockingGetch() ;
        }
    }

    return 0;
}

As I suggested there may be circumstances where you would not want the inner loop to run if an exit were requested, in which case:

//  Outer loop
while( ch != 'e' )
{
    ch = nonBlockingGetch() ;

    // inner loop
    while( ch != 'e' )
    {
        ch = nonBlockingGetch() ;
    }
}

Answer 4

You can try with user defined Interrupts