How do I?? Please Read this!!!! - Programmers Heaven

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How do I?? Please Read this!!!!


I think I have pretty much finished my source code for my second assignment. It is a menu driven program. I need a little help with one thing.

In module #2 the user is to type in a number.

If the user does not type in a number the program stops.

I need to constuct a invalid portion and I am not sure what I am doing wrong .

This is what I am typing in

program Primenumber;

uses crt;


n, trialdiv : integer;

prime : boolean;



write ('enter a number:');

readln (n);

If (n < integer) THEN


writeln('You have not selected a number');

writeln('Please try again');


this comes out as expected "(" at the THEN

Please if anyone can look this this over it would be great as it is due this afternoon.


[email protected]

Thank you very much


  • Try reading in a string and then test whether the string is an integer

  • : Try reading in a string and then test whether the string is an integer



    Thank you for replying.

    If I am reading in a string what would I do different in my readln.

    writeln('type in a number');


    would it be that I would declare the variable (n) as a string instead of a integer?

    And how would I test a string to see if it is a integer?

    Thanks again


  • You can declare N as a string type.

    Note that there is a pascal function called "val" which converts a string type to its numeric value. The function is something like this

    val(str : string, var int, code : integer);

    the code returns zero if the operation is successful, so maybe you can do something like this:


    N : string;

    number, code : integer;


    writeln('Enter a number');


    val(N, number, code);

    if code <> 0 then writeln('Invalid integer')

    else writeln('You have entered an integer');


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