do - while loop with multiple conditions in C - c

Question

I am trying to make a while - do loop to exit when the user types "exit" or "quit". For some reason that I can not understand, I simply can not make it happen. If I apply one of these conditions separately it works just fine, but I need to have both conditions simultaneously.
I searched online and I found several examples even on different programming languages, for example, (PHP) Do-While Loop with Multiple Conditions, (Python) How to do while loops with multiple conditions, (C++) Using multiple conditions in a do…while loop, etc. But no matter what procedure I am following I can make it work with both conditions simultaneously.
The ideal solution would be do add uppercase conditions also, but I can work with that later on as soon as I solve this problem.
Maybe a fresh pair of eyes see something that I am missing.
Sample of code is given below:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define MAX_CHARACTERS 250
#define MAX_USERNAME 12
#define MAX_USERS 1024
#define MIN_REQUIRED 3
#define MAX_PORT 65536
#define MIN_PORT 1
typedef struct rec {
char username[MAX_USERNAME];
char msg[MAX_CHARACTERS];
}RECORD;
/* Usage Instructions void because we do not have any return */
int help(void) {
printf("Usage: test.c [-s <arg0>] [-s <arg1>]\n");
printf("\t-s: a string program name <arg0>\n");
printf("\t-s: a string with a Nickname maximum characters %i <arg2>\n",MAX_USERNAME);
return (1);
}
int main(int argc, char **argv) {
if ( argc < MIN_REQUIRED ) {
printf ("Please follow the instructions: not less than %i argument inputs\n", MIN_REQUIRED);
return help();
}
else if ( argc > MIN_REQUIRED ) {
printf ("Please follow the instructions: not more than %i argument inputs\n", MIN_REQUIRED);
return help();
}
else {
RECORD *ptr_record;
ptr_record = (RECORD *) malloc (sizeof(RECORD));
if (ptr_record == NULL) {
printf("Out of memory!\nExit!\n");
exit(0);
}
char username_argv[MAX_USERNAME];
memset( username_argv, '\0', sizeof(username_argv) );
if (strlen(argv[2]) > 12 ) {
printf("Maximum characters for Nickname: %i\nPlease try again!\n", MAX_USERNAME);
exit(0);
}
strcpy( username_argv, argv[1] );
strncpy( (*ptr_record).username, username_argv, sizeof(username_argv) );
printf("Username pointer: %s\n", (*ptr_record).username);
do {
printf("Please enter your MSG: \n");
scanf ("%s", (*ptr_record).msg);
printf("User MSG: %s\n", (*ptr_record).msg);
//} while ((strcmp((*ptr_record).msg,"exit") != 0) || (strcmp((*ptr_record).msg, "quit") != 0));
//} while (strcmp((*ptr_record).msg, "exit") || strcmp((*ptr_record).msg, "quit") != 0);
//} while ((strcmp((*ptr_record).msg,"exit")) || (strcmp((*ptr_record).msg, "quit")) != 0);
//} while ((*ptr_record).msg != "quit" || (*ptr_record).msg != "exit");
} while (((*ptr_record).msg != exit) || ((*ptr_record).msg != ));
free(ptr_record);
return 0;
} /* End of else */
} /* End of main() */

Answer 1

Try:
} while ((strcmp((*ptr_record).msg,"exit") != 0) &&
(strcmp((*ptr_record).msg,"quit") != 0));
You want NOT (A OR B), not NOT A OR NOT B. Remember De Morgan's laws that say that NOT (A OR B) is the same as NOT A AND NOT B.
Using || is wrong as you will always have at least one condition (operand of ||) or another to be true.
Imagine you string is "exit" then:
(strcmp((*ptr_record).msg,"exit") != 0)
is false
but
(strcmp((*ptr_record).msg,"quit") != 0)
is true.
It means 0 || 1 which yields 1. Same (in the opposite) for the "quit" string (1 || 0 which yields 1). For other strings, both operand of || will be 1 and 1 || 1 yields 1.

Answer 2

It doesn't work, because you want to do the loop while the string is different from "exit" and the string is different from "quit".
If you use an OR, the condition will always be true, because the string can't have both values at the same time.
do {
printf("Please enter your MSG:\n");
scanf ("%s", (*ptr_record).msg);
printf("User MSG: %s\n", (*ptr_record).msg);
} while ((strcmp((*ptr_record).msg, "exit") != 0) && (strcmp((*ptr_record).msg, "quit") != 0));

Answer 3

All of the lines in your example use the logical OR operator || to test both conditions. Try to use the logical AND operator, &&, instead.
The problem with OR is that the way you've got it set up, the condition will always pass, so the application will never quit. If the user typed "quit", then the condition passes because he/she didn't type "exit". Likewise, if the user typed "exit", then he/she didn't type "quit", so the condition still passes. And, of course, if he/she didn't type either one, then the condition passes. That doesn't leave you with any way out of the loop.

Answer 4

Try out this. You should use the && operator because both the conditions need to be true to continue.
do {
printf("Please enter your MSG: \n");
scanf ("%s", (*ptr_record).msg);
printf("User MSG: %s\n", (*ptr_record).msg);
} while (((*ptr_record).msg != "exit") && ((*ptr_record).msg != "quit"));