Character Array comparison

magda3227 · 07-08-2008, 07:51 PM

I was wondering how I would go about checking a character array for a specific character that keeps changing.

What I want to do is compare the User input to the string. If the user does not pick one of the 6 letters, then they are prompted to do so again.

Code:

int i, j;
char Scenario[6]= {'A','B','C','D','E','F'};
char UserScenario='Z';


	while(UserScenario!=TGnScenario[i]) /*Obviously not right, but basically what I need, but how would I go about doing this?*/
	{
		printf("TGn scenario (A to F)?\t");
		scanf("%c", &UserScenario);
	}

I was thinking about using something like strchr, but my program ended up not doing anything. I don't know if it applies to this situation since I am comparing a character array, not really a string. This is probably really easy, but I am stuck on it.

Cactus_Hugger · 07-08-2008, 08:06 PM

Quote:

I don't know if it applies to this situation since I am comparing a character array, not really a string. This is probably really easy, but I am stuck on it.

You're right, strchr() requires a string. So why not make it one?

Code:

char Scenario[] = "ABCDEF";
...
strchr(Scenario, UserScenario)

Additionally, if your letters are always A-F, or something like that, this will work:

Code:

if(UserScenario >= 'A' && UserScenario <= 'F')

magda3227 · 07-09-2008, 06:19 AM

Hm. It's still not working. I tried using

Code:

if(UserScenario >= 'A' && UserScenario <= 'F')

and that didn't work. I also tried making my character array into a string and searching it. It doesn't work. I am getting an infinite loop or the program is bypassing it completely depending on small changes that I make. Any other suggestions?

Code:

int i, j;
char Scenario[6]= "ABCDEF";
char UserScenario='Z';
char *p;

p=strchr(Scenario,UserScenario);


 while(p!=NULL)
  {
	printf("scenario (A to F)?\t");
	scanf("%c", &UserScenario);
        p=strchr(p+1,UserScenario);
  }

	}

Am I not using strchr correctly? This is most likely the case...

matsp · 07-09-2008, 06:30 AM

Code:

char Scenario[6]= "ABCDEF";

That is an array that has exactly 6 elements. It is not guaranteed to be followed by a zero, so the strchr() may well continue reading beyond the end of your string. Either change the 6 to 7, or just remove it altogether.

Also strchr() returns NULL if you don't find something, so searching for Z and doing while(p != NULL) will lead to the loop never being entered.

Should you enter the above loop:

Code:

p=strchr(p+1,UserScenario);

would probably crash if p is NULL.

--
Mats

magda3227 · 07-09-2008, 06:43 AM

Thanks. This works...

Code:

char Scenario[7]="ABCDEF";
char UserScenario;
char *p=NULL;

 while(p==NULL)
  {
	printf("Scenario (A to F)?\t");
	scanf("%c", &UserScenario);
	p=strchr(Scenario,UserScenario);
  }

For some reason, if the user enters a letter not A-F, Scenario (A to F)? is printed twice though. Any idea as to why?

matsp · 07-09-2008, 06:48 AM

Quote:

Originally Posted by magda3227

For some reason, if the user enters a letter not A-F, Scenario (A to F)? is printed twice though. Any idea as to why?

The scanf() function reads one character. When you type A + Enter, the Enter is fed into the input buffer as a "newline" ('\n'). Next time you get to the scanf() it reads that newline, which of course isn't 'A'..'F', so it's rejected and you stay in the loop.

Putting a getchar() after scanf() would solve that problem.

--
Mats

magda3227 · 07-09-2008, 06:58 AM

Thank you very much matsp.

Elysia · 07-09-2008, 08:36 AM

I recommend writing
char Scenario[7]="ABCDEF";
...as...
char Scenario[]="ABCDEF";
To avoid subtle problems to determine the correct length and if you accidentally increase the length when forgetting to increase the size.

07-08-2008, 07:51 PM	#1
magda3227 Registered User Join Date: Jun 2008 Posts: 45	Character Array comparison I was wondering how I would go about checking a character array for a specific character that keeps changing. What I want to do is compare the User input to the string. If the user does not pick one of the 6 letters, then they are prompted to do so again. Code: int i, j; char Scenario[6]= {'A','B','C','D','E','F'}; char UserScenario='Z'; while(UserScenario!=TGnScenario[i]) /Obviously not right, but basically what I need, but how would I go about doing this?/ { printf("TGn scenario (A to F)?\t"); scanf("%c", &UserScenario); } I was thinking about using something like strchr, but my program ended up not doing anything. I don't know if it applies to this situation since I am comparing a character array, not really a string. This is probably really easy, but I am stuck on it. Last edited by magda3227; 07-08-2008 at 07:53 PM.
magda3227 is offline

07-09-2008, 06:19 AM	#3
magda3227 Registered User Join Date: Jun 2008 Posts: 45	Hm. It's still not working. I tried using Code: if(UserScenario >= 'A' && UserScenario <= 'F') and that didn't work. I also tried making my character array into a string and searching it. It doesn't work. I am getting an infinite loop or the program is bypassing it completely depending on small changes that I make. Any other suggestions? Code: int i, j; char Scenario[6]= "ABCDEF"; char UserScenario='Z'; char *p; p=strchr(Scenario,UserScenario); while(p!=NULL) { printf("scenario (A to F)?\t"); scanf("%c", &UserScenario); p=strchr(p+1,UserScenario); } } Am I not using strchr correctly? This is most likely the case...
magda3227 is offline

07-09-2008, 06:30 AM	#4
matsp Kernel hacker Join Date: Jul 2007 Location: Farncombe, Surrey, England Posts: 15,686	Code: char Scenario[6]= "ABCDEF"; That is an array that has exactly 6 elements. It is not guaranteed to be followed by a zero, so the strchr() may well continue reading beyond the end of your string. Either change the 6 to 7, or just remove it altogether. Also strchr() returns NULL if you don't find something, so searching for Z and doing while(p != NULL) will lead to the loop never being entered. Should you enter the above loop: Code: p=strchr(p+1,UserScenario); would probably crash if p is NULL. -- Mats __________________ Compilers can produce warnings - make the compiler programmers happy: Use them! Please don't PM me for help - and no, I don't do help over instant messengers.
matsp is offline

07-09-2008, 06:43 AM	#5
magda3227 Registered User Join Date: Jun 2008 Posts: 45	Thanks. This works... Code: char Scenario[7]="ABCDEF"; char UserScenario; char *p=NULL; while(p==NULL) { printf("Scenario (A to F)?\t"); scanf("%c", &UserScenario); p=strchr(Scenario,UserScenario); } For some reason, if the user enters a letter not A-F, Scenario (A to F)? is printed twice though. Any idea as to why?
magda3227 is offline

07-09-2008, 06:58 AM	#7
magda3227 Registered User Join Date: Jun 2008 Posts: 45	Thank you very much matsp.
magda3227 is offline

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Using a character array in a switch question.	bajanElf	C Programming	10	11-08-2008 08:06 AM
compare between a array of character and a pointer to an array of characters	steve1_rm	C Programming	7	05-11-2008 10:57 AM
Initialzing a 2D character array	mike_g	C Programming	3	08-16-2007 02:05 AM
Character Array - almost? works	voltson4	C Programming	3	03-04-2003 06:03 PM
Array of Character Arrays	Unregistered	C Programming	3	02-09-2002 06:07 PM