I need to print values that are in a matrix, these may vary from integer to real. As an example a matrix that my program use, named kernel, is shown below:
kernel[0,0]:= 1/16;
kernel[0,1]:= 2/16;
kernel[0,2]:= 1/16;
kernel[1,0]:= 2/16;
kernel[1,1]:= 4/16;
kernel[1,2]:= 2/16;
kernel[2,0]:= 1/16;
kernel[2,1]:= 2/16;
kernel[2,2]:= 1/16;
the issue comes when printing each of them, because I couldn't find a way to print a number like 1/16 in a easy-to-read way, the program displays something like 6.2500000000000000000000000000E-2 which is OK but I would prefer to have something more aesthetic like 0.0625 or even better 1/16. Does anyone acknowledge a way of formatting that allows me to do so?
Each array element holds the value of the fraction.
To write the value as a fraction you can simply calculate the numerator as the product of the array element and the denominator.
I prefer to use the Format() function for display formatting.
Given the array you show, two index variables, a and b and the denominator
denominator := 16;
for a := 0 to 2 do
for b := 0 to 2 do
begin
s := format('kernel[%d,%d] = %d/%d',[a,b,round(kernel[a,b]*denominator),denominator]);
memo1.Lines.Add(s);
end;
Related
procedure TForm1.Button1Click(Sender: TObject);
var
term1: integer;
term2: integer;
term3: integer;
j: integer;
begin
term1 := (0);
term2 := (1);
for j := 1 to 100 do;
begin
term3 :=( term1 + term2);
Memo1.Text:=inttostr(term3);
term1 := term2;
term2 := term3;
end;
end;
end.
This is what I have so far, but term1 and term2 don't want to add up. I have tried some different things, but for some reason the integers never want to add up.
There are several problems with your code
The semicolon after for j := 1 to 100 do prevents your next code that is withing begin..end block to be run in a loop. Why? The code that is to be run in each cycle of for loop is the one that follows the do until the first semicolon. Since you put semicolon just after the do this basically means that empty block of code is ran in a loop. Your begin..end block comes after that. Removing the semicolon after do will fix that.
You are using Memo1.Text:=inttostr(term3); to write the result into Memo. The problem with this is that this will rewrite entire text of the Memo every time so you will end up with only one line showing the last number. You should use Memo1.Lines.Add(inttostr(term3)); instead so that new line is added each time.
Lastly you are using Integer type for your variables. Since numbers in Fibonacci sequence grows very fast you will quickly exceed the maximum value that can be stored in Integer which in Delphi is Signed 32 bit Integer with a max value of 2147483647. You will have to use bigger integer types like 64 bit Integer type and since you are only dealing with positive numbers you should therefore use Unsigned 64 bit Integer that in declared in Delphi by UInt64 type. You can read more about Delphi default Integer types in documentation. Unfortunately not even UInt64 will is big enough for value of all first 100 numbers of Fibonacci sequence. So you will have to use one of the BigIntegers libraries for Delphi to do this properly. There are several of them available on internet.
You have an erroneous ; on your loop that you need to remove:
for j := 1 to 100 do;
^
Write a program to convert an integer number to its hexadecimal representation without using inbuilt functions.
Here is my code, but it is not working. Can anyone tell where is the mistake?
It is giving an error:
"Project raised exception class EAccessViolation with message 'Access violation at address 00453B7B in module 'Project.exe'.Write of address FFFFFFFF'.Process stopped.Use Step or Run to continue."
unit Unit1;
interface
uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls,Forms,
Dialogs;
type
TForm1 = class(TForm)
end;
function hexvalue(num:Integer):Char;
var
Form1: TForm1;
implementation
{$R *.dfm}
function hexvalue(num:Integer):Char;
begin
case num of
10: Result:='A';
11: Result:='B';
12: Result:='C';
13: Result:='D';
14: Result:='E';
15: Result:='F';
else Result:=Chr(num);
end;
end;
var
intnumber,hexnumber,actualhex:String;
integernum:Integer;
i,j,k:Byte;
begin
InputQuery ('Integer Number','Enter the integer number', intnumber);
integernum:=StrToInt(intnumber);
i:=0;
while integernum >= 16 do
begin
hexnumber[i]:=hexvalue(integernum mod 16);
integernum:= integernum div 16;
Inc(i);
end;
hexnumber[i]:= hexvalue(integernum);
k:=i;
for j:=0 to k do
begin
actualhex[j]:= hexnumber[i];
Dec(i);
end;
ShowMessage(actualhex);
end.
Since this obviously is a homework assignment, I don't want to spoil it for you and write the solution, but rather attempt to guide you to the solution.
User input
In real code you would need to be prepared for any mistake from the user and check that the input really is integer numbers only and politely ask the user to correct the input if erroneous.
Conversion loop
You have got that OK, using mod 16 for each nibble of integernum and div 16 to move to the next nibble, going from units towards higher order values.
Conversion of nibble to hex character
Here you go wrong. If you would have written out also the cases for 0..9, you could have got the case statement right. As others have commented, Chr() takes an ASCII code. However, using a case statement for such a simple conversion is tedious to write and not very efficient.
What if you would have a lookup table (array) where the index (0..15) directly would give you the corresponding hex character. That would be much simpler. Something like
const
HexChars: array[_.._] of Char = ('0',_____'F')
I leave it to you to fill in the missing parts.
Forming the result (hex string)
Your second major mistake and the reason for the AV is that you did not set the length of the string hexnumber before attempting to acess the character positions. Another design flaw is that you fill in hexnumber backwards. As a result you then need an extra loop where you reverse the order to the correct one.
There are at least two solutions to solve both problems:
Since you take 32 bit integer type input, the hex representation is not more than 8 characters. Thus you can preset the length of the string to 8 and fill it in from the lower order position using 8 - i as index. As a final step you can trim the string if you like.
Don't preset the length and just concatenate as you go in the loop hexnumber := HexChars[integernum mod 16] + hexnumber;.
Negative values
You did not in any way consider the possibility of negative values in your code, so I assume it wasn't part of the task.
First mistake : String are 1 indexed. Meaning that the index of their first character is 1 and not 0. You initialize "i" to 0 and then try to set hexnumber[i].
Second mistake : Strings might be dynamic, but they don't grow automatically. If you try to access the first character of an empty string, it won't work. You need to call SetLength(HeXNumber, NumberOfDigits). You can calculate the number of digits this way :
NumberOfDigits := Trunc(Log16(integernum)) + 1;
Since Log16 isn't really something that exists, you can either use LogN(16,integernum) or (Log(IntegerNum) / Log(16)) depending on what is available in your version of Delphi.
Note that this might return an invalid value for very, very large value (high INT64 range) due to rounding errors.
If you don't want to go that road, you could replace the instruction by
hexnumber := hexvalue(integernum mod 16) + hexnumber;
which would also remove the need to invert the string at the end.
Third Mistake : Using unsigned integer for loop variable. While this is debatable, the instruction
for I := 0 to Count - 1 do
is common practice in Delphi without checking Count > 0. When count = 0 and using an unsigned loop counter, you'll either get an integer overflow (if you have them activated in your project options) or you'll loop High(I) times, which isn't what you want to be doing.
Fourth mistake : already mentionned : Result:=Chr(num) should be replaced by something like Result := InttoStr(Num)[1].
Personally, I'd implement the function using an array.
HexArr : Array[0..15] of char = ('0', '1',...,'D','E','F');
begin
if InRange(Num, 0, 15) then
Result := HexArr[Num]
else
//whatever you want
end;
I am trying to write a program which will do multiply/divide the same variable without it resetting(sorry if it is not explained well). I will show an example if what I want
var
selection:integer
writeln ('Select a number');
readln (selection);
writeln (selection*10);
writeln (selection/5);
What I want to happen is for the selection variable to be multiplied by 10, then divided by 5. e.g. if the user enters 5, it will be multiplied by 10, then divided by 5. So I should get 5*10=50, then 50/5=10. But instead it will do 5*10, and then 5/5 separately.How would I do it so that it does the multiplication, and then the division to the new number made from the multiplication?
You aren't modifying the variable. You need to write it like this:
selection := selection * 10;
writeln(selection);
selection := selection div 5;
writeln(selection);
Note also that you need to use integer division, div, rather than real division, /.
How could i multiply a string by a number to achieve n amount of repetitions of that string in a Labels caption, i.e
if n = 5 then 's'*n= 'sssss' which would then become the labels caption.
anything along those lines returns the error that the operator is not applicable to the operand type.
thanks
There's no built in operator that does what you want. Your code would work in Python, but not in Delphi.
If your string is a single character then you can use StringOfChar:
Caption := StringOfChar('s', n);
For a longer input string use DupeString from the StrUtils unit:
Caption := DupeString('blah', n);
Delphi does not allow that syntax. However, there is a function called DupeString, in StrUtils.pas that amounts to the same thing:
Label1.Caption := DupeString('test', 4);
How can I create a random 64-bit integer value in Delphi 2006? The built-in integer-based Random() function seems to return only values between 0 and 2^31.
You can use my GpRandomGen. It implements Marsaglia/Zaman/James algorithm, is extremely fast and supposedly very random. Released as a freeware.
Generate two 32 bit randoms and splice them together.
EDIT
Similar to #Andreas's answer I like the following (equivalent) implementation:
function Random64: UInt64;
var
Overlay: packed record
a, b: UInt32;
end absolute Result;
begin
Assert(SizeOf(Overlay)=SizeOf(Result));
Overlay.a := Random32;
Overlay.b := Random32;
end;
To answer my own question I came up with the following code:
function GetRandomInt64() : int64;
begin
Int64Rec(result).Words[0] := Random(High(Word));
Int64Rec(result).Words[1] := Random(High(Word));
Int64Rec(result).Words[2] := Random(High(Word));
Int64Rec(result).Words[3] := Random(High(Word));
end;
Not sure if this is a valid solution or it will always create the same follow-up number X+1 after a given result number X.
You can generate 64 random bits and interpret the result as an integer. (63 bits if you are working with signed integers and want the result to be non-negative.) Equivalently you can take two random integers in the range 0..2^31-1, plus two extra random bits, and concatenate them to get a random 64-bit integer.
EDIT: I was curious about the statistical properties of pseudo-random numbers generated by concatenating pseudo-random components and found that (apparently) this approach might not work well depending on your pseudo-random generator (of course for true random number generation, as from atmospheric noise, concatenating random bits is no problem). For recreational use, the loss of various statistical properties might be acceptable, but for more serious use you might end up needing a custom pseudo-random generator as #gabr suggested. Here is a related question: Best method of generating a number with 256 random bits?
Create a GUID (eg CoCreateGuid) and cast it to Int64.
Simple:
function Random64: UInt64;
begin
PCardinal(#result)^ := Random32;
PCardinal(cardinal(#result) + 4)^ := Random32;
end;
where Random32 is your favourite 32-bit unsigned integer random number function.