Thread: I need help with validation for two inputs

Hello, I am having trouble with error checking on my program that has two inputs. The first is a menu selection, and the second is an amount greater than 0. For both inputs it must check against entering a letter or an invalid number. I tried a do/while statement for the menu selection, and that took care of the valid menu option part, but I can't seem to figure out how to handle a character input.

I tried to use isdigit to solve this problem, but I may not have implemented it correctly. If you guys could take a look at my code and maybe give some advice on what would be the best way to tackle this problem.

Code:

#include <stdio.h>
#include <ctype.h>

	main()
	
	 {
	 	char iSelection;
	 	float fCurrSelect = 0.00;
	 	float fUSCurr = 0.00;
	 	
	 do {
	 	
	 	printf("\n\tCurrency Conversion Program 1.1\n\n");
	 	printf("\nChoose the currency you wish to convert\n");
	 	printf("\n1\tAustrailian dollar");
	 	printf("\n2\tCanadian dollar");
	 	printf("\n3\tEuro");
	 	printf("\n4\tMexican peso");
	 	printf("\n5\tSwiss franc\n\n");
	 	scanf("%d", &iSelection);
	 		
	 	} while (iSelection < 1 || iSelection > 5);  
	 	 	   
	 
	 	printf("\nHow much money would you like to convert to U.S. dollars?");
	 	scanf("%f", &fCurrSelect);
	 	   
	 	  
	 	   
	 	   
	 	switch(iSelection) {
	 	   
	 	      case 1:
	 	      fUSCurr = (fCurrSelect/1.16686);
	 	      printf("\nThe Austrailian dollar amount %.2f converted to USD equals $%.2f", fCurrSelect, fUSCurr);
	 	      break;
	 	      
	 	      case 2:
	 	      fUSCurr = (fCurrSelect/1.0072);
	 	      printf("\nThe Canadian dollar amount %.2f converted to USD equals $%.2f", fCurrSelect, fUSCurr);
	 	      break;
	 	      
	 	      case 3:
	 	      fUSCurr = (fCurrSelect/0.695943);
	 	      printf("\nThe Euro amount %.2f converted to USD equals $%.2f", fCurrSelect, fUSCurr);
	 	      break;
	 	      
	 	      case 4:
	 	      fUSCurr = (fCurrSelect/10.8509);
	 	      printf("\nThe Mexican peso amount %.2f converted to USD equals $%.2f", fCurrSelect, fUSCurr);
	 	      break;
	 	      
	 	      case 5:
	 	      fUSCurr = (fCurrSelect/1.1522);
	 	      printf("\nThe Swiss franc amount %.2f converted to USD equals $%.2f", fCurrSelect, fUSCurr);
	 	      break;
	 	      
	 	      default:
	 	      printf("\nInvalid option!");
	 	      
	 	   }//end switch block
	 	   getchar();
	  }//end main

Your code is not indented correctly. Please correct it (you have an error where the do... while loop ends.

Here's the new indented code with some corrections (int main(), return 0):

Code:

#include <stdio.h>
#include <ctype.h>

int main(void)
{
	char iSelection;
	float fCurrSelect = 0.00;
	float fUSCurr = 0.00;
	 	
	do 
	{
		printf("\n\tCurrency Conversion Program 1.1\n\n");
	 	printf("\nChoose the currency you wish to convert\n");
	 	printf("\n1\tAustrailian dollar");
	 	printf("\n2\tCanadian dollar");
	 	printf("\n3\tEuro");
	 	printf("\n4\tMexican peso");
	 	printf("\n5\tSwiss franc\n\n");
	 	scanf("&#37;d", &iSelection);
	} while (iSelection < 1 || iSelection > 5);  
	 	 	   
	 
	printf("\nHow much money would you like to convert to U.S. dollars?");
	scanf("%f", &fCurrSelect);
		 	   
	 	   
	switch(iSelection) 
	{
		case 1:
	 		fUSCurr = (fCurrSelect/1.16686);
	 		printf("\nThe Austrailian dollar amount %.2f converted to USD equals $%.2f", fCurrSelect, fUSCurr);
	 		break;
	 	      
	 	case 2:
	 		fUSCurr = (fCurrSelect/1.0072);
	 		printf("\nThe Canadian dollar amount %.2f converted to USD equals $%.2f", fCurrSelect, fUSCurr);
	 		break;
	 	      
	 	case 3:
	 		fUSCurr = (fCurrSelect/0.695943);
	 		printf("\nThe Euro amount %.2f converted to USD equals $%.2f", fCurrSelect, fUSCurr);
	 		break;
	 	      
	 	case 4:
	 		fUSCurr = (fCurrSelect/10.8509);
	 		printf("\nThe Mexican peso amount %.2f converted to USD equals $%.2f", fCurrSelect, fUSCurr);
	 		break;
	 	      
	 	case 5:
	 		fUSCurr = (fCurrSelect/1.1522);
	 		printf("\nThe Swiss franc amount %.2f converted to USD equals $%.2f", fCurrSelect, fUSCurr);
	 		break;
	 	      
	 	default:
	 		printf("\nInvalid option!");
	}//end switch block
	getchar();
	return 0;
}//end main

Now I can actually take a look at the code!

Sorry about the indentation, as you can tell I am rather new to this I forgot to switch back the iSelection to int after messing with it. I was trying the isdigit to verify that a digit was entered. The problem that I am having is that we are suppose to have the input checked to make sure that someone doesn't enter a letter, and for the monetary value it should be greater than 0 and not be a letter. When you enter a letter it just loops infinitely, obviously due to the fact I have no error check for this.

I would think that isdigit should fix the problem, but I am not sure how to add that in properly. I tried to add it in with my while statement, but it didn't seem to do anything. Thanks for the replies guys, I really appreciate the help.

Thank you so much for the replies guys. We never really covered anything about error handling in our text, and the teacher is not so speedy with getting back to us with questions. I like how we get assignments that are more advanced than the material that we cover I guess I will have to do some research on fgets, strtol, and strtod. Thanks again!

Ok, I have tried some new things and I think I am getting close. I used an if statement and it seems to check the validation of the entry. The only thing is that when a valid entry is made, it goes right to the calculation part of my code, and skips the second input part.

I am also not sure how to return back to the menu selection after a choice has been made, the program just finishes either way. Here is the updated code:

Code:

#include <stdio.h>
#include <ctype.h>

	main()
	
	 {
	 	char iSelection = '\0';
	 	float fCurrSelect = 0.00;
	 	float fUSCurr = 0.00; 	
	 	 	
	 	printf("\n\tCurrency Conversion Program 1.1\n\n");
	 	printf("\nChoose the currency you wish to convert\n");
	 	printf("\n1\tAustrailian dollar");
	 	printf("\n2\tCanadian dollar");
	 	printf("\n3\tEuro");
	 	printf("\n4\tMexican peso");
	 	printf("\n5\tSwiss franc\n\n");
	 	scanf("%c", &iSelection); 		
	   	 	 	   
	 	if (isdigit(iSelection)&& iSelection >= 1 && iSelection <= 5){
	 	printf("\nHow much money would you like to convert to U.S. dollars?");
	 	scanf("%f", &fCurrSelect);
	 		 	
	 	}//end if statement 
	 	   
	 	switch(iSelection) {
	 	   
	 	      case '1':
	 	      fUSCurr = (fCurrSelect/1.16686);
	 	      printf("\nThe Austrailian dollar amount %.2f converted to USD equals $%.2f", fCurrSelect, fUSCurr);
	 	      break;
	 	      
	 	      case '2':
	 	      fUSCurr = (fCurrSelect/1.0072);
	 	      printf("\nThe Canadian dollar amount %.2f converted to USD equals $%.2f", fCurrSelect, fUSCurr);
	 	      break;
	 	      
	 	      case '3':
	 	      fUSCurr = (fCurrSelect/0.695943);
	 	      printf("\nThe Euro amount %.2f converted to USD equals $%.2f", fCurrSelect, fUSCurr);
	 	      break;
	 	      
	 	      case '4':
	 	      fUSCurr = (fCurrSelect/10.8509);
	 	      printf("\nThe Mexican peso amount %.2f converted to USD equals $%.2f", fCurrSelect, fUSCurr);
	 	      break;
	 	      
	 	      case '5':
	 	      fUSCurr = (fCurrSelect/1.1522);
	 	      printf("\nThe Swiss franc amount %.2f converted to USD equals $%.2f", fCurrSelect, fUSCurr);
	 	      break;
	 	      
	 	      default:
	 	      printf("\nInvalid option!");
	 	      
	 	   }//end switch block
	 	   getchar();
	 	   return 0;
	  }//end main

Ah, I guess I didn't know that about the isdigit function. I think I am one step closer to getting this program to where I like it. I chose to go back with the do/while statement, and I also added a do/while for the monetary value entered. It now checks for letters and invalid digits. The only weird thing is that it seems like the menu loops twice when a wrong input is given. Here is just the part of the code that I was having trouble with, I am sorry for cluttering up the thread:

Code:

int main(void)
	
	 {
	 	char iSelection = '\0';
	 	float fCurrSelect = 0.00;
	 	float fUSCurr = 0.00;
	 	
	 	do { 	
	 	 	
	 	printf("\n\tCurrency Conversion Program 1.1\n\n");
	 	printf("\nChoose the currency you wish to convert\n");
	 	printf("\n1\tAustrailian dollar");
	 	printf("\n2\tCanadian dollar");
	 	printf("\n3\tEuro");
	 	printf("\n4\tMexican peso");
	 	printf("\n5\tSwiss franc\n\n");
	 	scanf("%c", &iSelection); 		
	   	 	 	   
	 	}while ( iSelection < '1' || iSelection > '5');
	 	
	 	do {
	 	printf("\nHow much money would you like to convert to U.S. dollars?");
	 	scanf("%f", &fCurrSelect);
	 	}while (fCurrSelect <= 0.0);

I will work on having an exit type so that the user may continue to use the program without having to re-run it. Would a flag be used in that sort of situation?

Thank you so much matsp for the replies. It seems as if once I figure one thing out, there is a plethora of more things right inside of it to confuse me I will have to try some more tweaking and experimenting to see what I can come up with.

Also, how would I have an error message shown if the user makes a wrong selection. I am guessing that it would have to be inside the do/while block because if it is outside it just prints the error message when a valid entry is made. I will play around with this for a bit too, and see what I get.