Need Help Modifying Code

sosy2001 · #1 08-Nov-2004, 04:08

I need to modify this code so that if anything other than a digit is typed, the input is considered to be an error. I tried several codes, but I have not been successful. Can someone offer some help?

CPP / C++ / C Code:

do
{
	printf("Input a positive integer:  ");
	fgets(line, MAXLINE, stdin);
	error = sscanf(line, "%d", &n) != 1 || n <= 0 ;
	if (error)
		printf("\nERROR: Do it again.\n");
} while (error)

dsmith · #2 08-Nov-2004, 06:50

Hi sosy2001. The code works fine for me, except in cases where a real value is entered. I added a strchr command to look for a decimal. I also added a semicolon after the while statement (necessary to compile) and put it into a small program. Works fine. The logic seems sound and it is pretty efficient.

CPP / C++ / C Code:

#include <stdio.h>
#define MAXLINE 100
int main()
{

int n, error;
char line[MAXLINE];

	do{
		printf("Input a positive integer:  ");
		fgets(line, MAXLINE, stdin);
		error = sscanf(line, "%d", &n) != 1 || n <= 0 || strchr(line,'.');
		if (error)
			printf("\nERROR: Do it again.\n");
	} while (error);		//Semicolon missing....
}

Cheers.

davekw7x · #3 08-Nov-2004, 08:27

Quote:

Originally Posted by sosy2001

I need to modify this code so that if anything other than a digit is typed, the input is considered to be an error.

Can you be a little more specific?

For example, what if the user enters 123a

Is this OK (with the integer value = 123, and everything else discarded)?

Regards,

Dave

dsmith · #4 08-Nov-2004, 18:41

Hi sosy2001. I am sorry! I didn't fully test that! I was so enamored with the logic that I overlooked full testing!!!!

Unfortunately, I couldn't figure out how to make it work the way you had it. There may be a much better solution than this, but this is what I came up with:

CPP / C++ / C Code:

#include <stdio.h>
#define MAXLINE 100


int main()
{

int n, error;
char line[MAXLINE];

	do{
		printf("Input a positive integer:  ");
		fgets(line, MAXLINE, stdin);
		error = 0;
		for(n=0;line[n] && !error;n++)
			error = (isdigit(line[n]) == 0) && (line[n] != 10);
		if (error)
			printf("\nERROR: Do it again.\n");
	} while (error);		//Semicolon missing....
}

Again, I am sorry about that. It is easy to see how important thorough testing is

sosy2001 · #5 09-Nov-2004, 14:11

This code did not work either. The main focus of this code is sscanf, and to print only integers or display the error message.

Sorry for being so complicated.And thanks for your assistance.

dsmith · #6 10-Nov-2004, 06:59

Hi sosy2001. Just curious, did the code not work or is it not acceptable because it does not use sscanf? I am certainly not above bad programs (I write them everyday

), but that code compiled and worked for every input that I threw at it.

If it is that sscanf is required, I will take a look at that and see if I can think of a way to do that...

sosy2001 · #7 10-Nov-2004, 17:26

I tried to use it but i got some error messages. I will foward these error messages to you in a few minutes.

Thanks.

sosy2001

sosy2001 · #8 10-Nov-2004, 18:16

First the assignment question:

Examine the typical use of sscanf().Write a program that prompts the user to input a positive integer. Guard against errors so that a string typed by the user is picked up.

CPP / C++ / C Code:

char line[MAXLINE];
	int error, n;
  do{
    printf("Input a positive integer:  ");
    fgets(line, MAXLINE, stdin);
              error = sscanf(line, "%d",&n) !=1||n<=0;
    if (error)

      printf("\nERROR: Do it again.\n");
  } while (error);

athus doesnot catch all the errors. For example 12X in typed instead of 123, the error is not caught. So I have to modify this code to fix this problem.

WaltP · #9 10-Nov-2004, 21:44

Quote:

Originally Posted by sosy2001

First the assignment question:

Examine the typical use of sscanf().Write a program that prompts the user to input a positive integer. Guard against errors so that a string typed by the user is picked up.

CPP / C++ / C Code:

char line[MAXLINE];
	int error, n;
  do{
    printf("Input a positive integer:  ");
    fgets(line, MAXLINE, stdin);
              error = sscanf(line, "%d",&n) !=1||n<=0;
    if (error)

      printf("\nERROR: Do it again.\n");
  } while (error);

athus doesnot catch all the errors. For example 12X in typed instead of 123, the error is not caught. So I have to modify this code to fix this problem.

Actually, you don't have an error as far as sscanf() is concerned. It converted what it could and stopped and the first non-digit character. I did some testing, and sscanf() will not see "23x" as an error because the '23' returns the value 1 and 'n' is 23. The 'x' is simply the character that determins the end of the number.

You might try

CPP / C++ / C Code:

error = sscanf(line, "%d%c",&n, &c);

and check c for whitespace (space,tab,CR,LF) and if it's not you have your error.

Also, your statement

CPP / C++ / C Code:

error = sscanf(line, "%d",&n) !=1||n<=0;
if (error)

can cause problems. It would probably be better to convert this into:

CPP / C++ / C Code:

error = sscanf(line, "%d",&n);
if (error  != 1 || n <= 0)

It's more understandable and accomplishes the same thing.

sosy2001 · #10 17-Nov-2004, 04:02

This program is written in five different files. I keep getting an error message and I cant figure out what it means. Can you help me please. Here is the error message I get:
ay.obj : error LNK2001: unresolved external symbol _report_a_loss
Debug/prn1.exe : fatal error LNK1120: 1 unresolved externals
Error executing link.exe.

prn1.exe - 2 error(s), 0 warning(s)

--------------------------------------------------------------------------

CPP / C++ / C Code:

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

#define MAXWORD 100

int    get_call_from_user(void);
void   play(int how_many);
void   prn_final_report(int win, int lose, int how_many);
void   prn_instructions(void);
void   report_a_win(int coin);
void   report_a_loss(int coin);
int    toss(void);
----------------------------------------------------------------------
include "heads.h"

int main(void)
{
   char   ans;
   int    no_of_plays;

   printf("\n"
      "THE GAME OF HEADS OR TAILS\n"
      "\n"
      "Do you want instructions?  ");
   scanf(" %c", &ans);
   putchar('\n');
   if (ans == 'y' || ans == 'Y')
      prn_instructions();
   printf("How many times do you want to play?  ");
   scanf("%d", & no_of_plays);
   putchar('\n');
   play( no_of_plays);
   return 0;
}
-------------------------------------------------------------------
#include "heads.h"
  void report_a_win(int coin)
{
	printf("You win, it was a");
	if (coin)
	{
		printf("tail\n");
	}
	else
	{
		printf("head\n");
	}
	return;
}

void report_a_lose(int coin)
{
	printf("You lose, it was a");
	if (coin)
	{
		printf("tail\n");
	}
	else
	{
		printf("head\n");
	}
	return;
}  

int toss(void)
{
   return (rand() % 2);     /* 0 = heads, 1 = tails */
}
-----------------------------------------------------------------------
#include "heads.h"

int get_call_from_user(void)
{
   int   guess;                /* 0 = heads, 1 = tails */

   do {
      printf("Call it:  ");
      if (scanf("%d", &guess) != 1) {
         printf("\nSORRY: Severe input error - bye!\n\n");
         exit(1);
      }
      if (guess != 0 && guess != 1) {
         printf("\n%s\n\n",
            "ERROR: Type 0 for heads, 1 for tails.");
      }
   } while (guess != 0 && guess != 1);
   return guess;
}
-------------------------------------------------------------------
#include "heads.h"

void prn_instructions(void)
{
   printf("%s\n",
      "This is the game of calling heads or tails.\n"
      "I will flip a coin; you call it.  If you\n"
      "call it correctly, you win; otherwise,\n"
      "I win.\n"
      "\n"
      "As I toss the (simulated) coin, I will\n"
      "tell you to \"call it.\"  To call heads,\n"
      "type 0; to call tails, type 1.\n"
      "\n");
}

void prn_final_report(int win, int lose, int how_many)
{
   printf("\n%s\n%s%3d\n%s%3d\n%s%3d\n\n",
      "FINAL REPORT:",
      "   Number of games that you won:  ", win,
      "   Number of games that you lost: ", lose,
      "   Total number of games:         ", how_many);
}

-----------------------------------------------------------------------

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search
Rate This Thread
Rate This Thread:

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Re: Formatting C / C++ code	WaltP	C Programming Language	1	06-Jan-2008 23:59
getting pWned by this code	quasimof	C++ Forum	1	21-Oct-2004 22:30
very difficult code - program	gaurav_sting	C++ Forum	1	16-Jun-2004 00:59
Explain code in MS STL's binary_search	rom	C++ Forum	11	07-Mar-2004 20:11

Need Help Modifying Code

Need More Help

I got errors

Here Is the Error

I have an error in my code I can't figure it out