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.

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')

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...

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

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?

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

Thank you very much matsp.

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.