Programming in C. Data validation and converting characters into integers

Question

I am making a program that includes a simple switch condition.

The problem I have encountered is that I am also validating user input so that the user cannot break the program by entering a character.

The switch works fine when I remove the isdigit() so I know it is something happening with data validation.

What I was told to do was use %c in my scanf() but if I do that then something else prevents the program from working. I suspect that it is because the switch is no longer is being referenced since the cases are 1,2,3...

The way I want to do it is just turn the character back into an integer before it reaches the switch but I am not sure how I could do that.

Something is happening when I copy and paste parts of the program so I will just paste the entire program.

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

int main(void)
{
   int BusRoute, LTrigger;
   char StartLoc,DestLoc;

   LTrigger = 1;
   BusRoute = 0;
   StartLoc = 0;
   DestLoc = 0;

   while (LTrigger >= 1)
   {
//Give user a menu and prompt to select input for BusRoute
   printf("\n\n\tPlease only use the numbers provided.");
   printf("\n\n  1.\n\tRoute_1\tCherokee Park and KFC YUM Center transit.");
   printf("\n\n  2.\n\tRoute_2\tUL and Cherokee Park transit.");
   printf("\n\n  3.\n\tRoute_3\tUL and KFC YUM Center transit.");
   printf("\n\n\n\t Please select one route from the above menu.");
   printf(" \n\n\tOnly use the single digit corresponding to the route: ");
   scanf("%d" , &BusRoute);

//Refresh window      
   system("cls");    

   if(isdigit(BusRoute))
   {
//Use switch to determin user's Route. Then present choice of To/From          
  switch (BusRoute)
             {         
        case 1:
        printf("\n\n\tYou have chosen Cherokee Park and KFC YUM Center transit.");
        printf("\n\n\tIf you want to travel from Cherokee Park to KFC YUM Center enter C.");
        printf("\n\n\tIf you want to travel from KFC YUM Center to Cherokee Park enter K.");
        printf("\n\n\tEnter your seletion now: ");
        scanf("%c" , &StartLoc);                                                           
        break;

//give two if statements to determine users location and confirm destination
        if (StartLoc == 'c' || StartLoc == 'C')
        {
        printf("\n\n\tYou have chosen to travel from Cherokee Park to KFC YUM Center.");
        printf("\n\n\tTo confirm you want to travel from Cherokee Park to KFC YUM Center please enter K: ");
        scanf("%c" , DestLoc);
//refresh           
        system("cls");  

 //confirmation of destination
         if (DestLoc == 'k' || DestLoc == 'K')
          {
               printf("\n\n\tYour bus route will pick you up from Cherokee Park and take you to KFC YUM Center.");
               getch();
           }//end dest                                                    
          }//end start

          //false user input           
             else
             {
               printf("\n\n\tYou did not enter a correct character.\n\n\tPress enter and only enter specific values.");
               getch();

                   //reset loop and refresh
               LTrigger = 1;
               system("cls");
               }//end else


          case 2:
          printf("\n\n\tYou have chosen Cherokee Park and UL transit.");
          break;

          case 3:
          printf("\n\n\tYou have chosen UL and KFC YUM Center transit.");
          break;

             }//end switch
      }//end if
               else
               {
                   printf("\n\n\tYou did not enter a number.\n\n\tPress enter and only enter specific values.");
                   getch();

                   //reset loop and refresh
                   LTrigger = 1;
                   system("cls");
                }//end else
      }//end loop

      getch();

 }//end main

rodrigo · Accepted Answer · 2012-09-11 23:06:27Z

3

isdigit takes a character and says if it is a character between '0' and '9'. But you are passing it an integer, not a character, so its output is meaningless.

If you want to know if the scanf succeeded, just check its return value: it will be 1 if it worked, or 0 if it failed (actually it will return the number of variables assigned):

if (scanf("%d", &BusRoute) > 0)
{

If you want to know if BusRoute is one digit long, then you can simply check it to be between 0 and 9 (or 3), but there is no need to do that: instead, add a default: clause to your switch.

BTW, you have missed a & in the line

scanf("%c" , DestLoc);

It should be:

scanf("%c" , &DestLoc);

Also, it is usually a good idea to add a space before the %c it will eat out any space or carriage return left in the buffer (from the previous user operation, for instance):

scanf(" %c" , &DestLoc);

Ditto, for the StartLoc case.

edited Sep 11, 2012 at 23:06

answered Sep 11, 2012 at 23:00

rodrigo

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4 Comments

Ev00 Over a year ago

I see thank you. As I have not been able to analyze that part of the code in a while I haven't gotten around to analying syntax errors haha derp. Thank you for your assistance.

Ev00 Over a year ago

After some practice I have discovered C does not allow default: arguments. I am stuck once again trying to insure a user cannot break the program by enter a character.

Jonathan Leffler Over a year ago

Of course, isdigit() will work fine as long as the user types a number between 48 and 57 (for 0 to 9)...but it is a bit unkind to make the user type raw ASCII codes in decimal.

Zan Lynx Over a year ago

@Ev00: Of course C allows default: in a switch statement. Not case default: Just default:

Dan Hauer · Accepted Answer · 2012-09-11 22:58:06Z

1

It's tricky to answer this without seeing your code. You can turn a character into an integer with a typecast:

switch((int) variable)

If variable is a character entered by the user, the typecast (int) will convert it to its ASCII code for the switch. Usually, though, C doesn't require typecasts to interpret characters as integers.

answered Sep 11, 2012 at 22:58

Dan Hauer

1113 bronze badges

Comments

Rami Jarrar · Accepted Answer · 2012-09-11 23:00:21Z

0

Look At this:

char charBusRoute;
int BusRoute;

/* ... */

scanf("%c",&charBusRoute);

if(isdigit(charBusRoute)){
    BusRoute = charBusRoute - '0';
    /* ... */
}

answered Sep 11, 2012 at 23:00

Rami Jarrar

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