Solved

avoiding integer run time errors

Posted on 2000-03-03
11
173 Views
Last Modified: 2010-04-16
HOW DO I STOP THE PROGRAM FROM FAILING IF A NON-NUMERICAL CHARACTER IS ENTERED ie NOT AN INTEGER ?????

 

VAR

CHOICE INTEGER

{MAIN PROGRAM BODY}


begin
        choice:= 10;
        while choice <> 9 do
        begin
        clrscr;
        showmenu;
        readln(choice);
        case choice of
        1: CREATEPERMANENTFILE;
        2: VIEW;
        3: entercostumedetails;
        4: ENTERCUSTOMERDETAILS;
        5: ENTERCUSTOMERORDER;
        6: SHOWALLCUSTOMERORDERS;
        7: SEARCHDATEORDER;
        8: SEARCHCNUMORDER;
        end;
        end;

I'm not allowed to change the choice to a char !!!!!!
0
Comment
Question by:elniniokev
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
11 Comments
 
LVL 12

Expert Comment

by:Hypo
ID: 2582160
you can use the command val...

Procedure Val(S: string; var V,Code : integer);

S is a string wich you want to convert to an integer, V is the target variable, and Code contains the possible error code!

Ok, so you might wonder why you want to use this function? I'll tell you why.

When you use readln(choice) and choice is an integer... the program will halt with an error code if you don't input a valid integer string.

But if you use a string instead of an integer in the readln procedure... You can enter whatever you like without have to worry about error messages halting the program! Also, the Val procedure converts a string into an integer variable and leaving an error code in a variable if the string is not a valid integer string.

So... to replace this process  [readln(choice)], you need 2 more variables except choice. One called St, of type string (St : string;) and one called Code, of type integer (Code : integer;)
St will contain the string you get from the Readln, Code will contain the error code (if any), and Choice will contain... the users choice!!!

This is how you could use it.

readln(St);
val(St,Choice,Code);
If Code <> 0 then ... {Do something to handle the error!}

And this is what your code would look like!

VAR

CHOICE,
CODE : INTEGER;
ST : STRING;

{MAIN PROGRAM BODY}

begin
        choice:= 10;
        while choice <> 9 do
        begin
        clrscr;
        showmenu;
        readln(St);
        Val(St,Choice,Code);
        If Code <> 0 then Choice := 10;
        case choice of
        1: CREATEPERMANENTFILE;
        2: VIEW;
        3: entercostumedetails;
        4: ENTERCUSTOMERDETAILS;
        5: ENTERCUSTOMERORDER;
        6: SHOWALLCUSTOMERORDERS;
        7: SEARCHDATEORDER;
        8: SEARCHCNUMORDER;
        end;
        end;

That should work just fine... If you don't enter a valid integer string... the program does nothing!

Hope it works!
0
 
LVL 1

Author Comment

by:elniniokev
ID: 2583443
the code didn't accept the choic e 1..9
an error was displyed
0
 
LVL 3

Expert Comment

by:Alisher_N
ID: 2583516
run-time error ?
what exactly ?
hypo's code must work fine
0
Enroll in June's Course of the Month

June's Course of the Month is now available! Every 10 seconds, a consumer gets hit with ransomware. Refresh your knowledge of ransomware best practices by enrolling in this month's complimentary course for Premium Members, Team Accounts, and Qualified Experts.

 
LVL 1

Author Comment

by:elniniokev
ID: 2584032
the program doesn't accept the choices between 1 & 9, the error message I added is displayed no matter what I enter. I'm new to programming it could be something with the placement of the code any more help would be greatly appreciated.
0
 
LVL 1

Author Comment

by:elniniokev
ID: 2584037
The Readln(st) is in the procedure showmenu as well as the main body code, I didn't understand why I have to have procedure val and what else it should contain.
0
 
LVL 1

Author Comment

by:elniniokev
ID: 2584039
Adjusted points to 40
0
 
LVL 12

Accepted Solution

by:
Hypo earned 40 total points
ID: 2584147
You have to use the procedure val since it returns an errorcode in the Code parameter instead of halting the entire program as readln does if there's an error in the input.

If you don't enter an integer in val(st,choice,code) the "code" variable  will contain a non zero value... If you don't enter an integer in readln(Choice) the program will halt with a runtime error. You didn't want that to happen... that's why you should use procedure val!
0
 
LVL 3

Expert Comment

by:sumant032199
ID: 2584420
{
   This is good working example of how you can eliminate error
   occuring due to input of invalid number.
   This function is verymuch similar to sscanf() in C.

}

program validint;
uses crt;

var str : string[10];
    int : integer;

function give_int(s : string) : integer;
var n,i : integer;
begin
    i:=1;
    n:=0;
    if not (s[i] in ['0'..'9','-']) then n := -1
    else
    begin
        if s[i] = '-' then i:=2;
        while s[i] in ['0'..'9'] do
        begin
              n := (n * 10) + ord(s[i]) - 48;
              i := i + 1;
        end;
    end;
    if s[1] = '-' then give_int := -n
    else give_int := n;
end;

begin
     clrscr;
     write('Enter a number: ');
     readln(str);

     str[length(str)+1] := #0;
     int := give_int(str);

     write('The number is: ',int);
end.
0
 
LVL 1

Author Comment

by:elniniokev
ID: 2585030
Hypo,  please re-submit your answer I got your code working and I want to give you the points you deserve. Thanks a million!!!!!
0
 
LVL 12

Expert Comment

by:Hypo
ID: 2585638
I can't answer this quizz as long as Sumant has proposed an answer to it. But I think that you can accept one of my comments as the answer? If you can't do that you have to reject Sumants answer first before I can propose an answer to it.

Anyway, I'm glad you got it to work.

regards Hypo.
0
 
LVL 1

Author Comment

by:elniniokev
ID: 2585775
Hypo's code is the one I'm using, I was wrong to reject it initialy. Sumant's answer is very good and shouldn't regard this as a rejection. Hypo's code was correct initially, it was me who stuffed up in the placement of the code he supplied.

Thanks to both !

0

Featured Post

On Demand Webinar - Networking for the Cloud Era

This webinar discusses:
-Common barriers companies experience when moving to the cloud
-How SD-WAN changes the way we look at networks
-Best practices customers should employ moving forward with cloud migration
-What happens behind the scenes of SteelConnect’s one-click button

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

In this post we will be converting StringData saved within a text file into a hash table. This can be further used in a PowerShell script for replacing settings that are dynamic in nature from environment to environment.
This article provides a convenient collection of links to Microsoft provided Security Patches for operating systems that have reached their End of Life support cycle. Included operating systems covered by this article are Windows XP,  Windows Server…
Monitoring a network: why having a policy is the best policy? Michael Kulchisky, MCSE, MCSA, MCP, VTSP, VSP, CCSP outlines the enormous benefits of having a policy-based approach when monitoring medium and large networks. Software utilized in this v…
Add bar graphs to Access queries using Unicode block characters. Graphs appear on every record in the color you want. Give life to numbers. Hopes this gives you ideas on visualizing your data in new ways ~ Create a calculated field in a query: …

687 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question