Noob help:

[barrydocks]

So I am trying to learn Lazerus, I am working through Start Programming Using Object Pascal but i seem to have stumbled at one of the first hurdles: when I use var: Single as in this code:

Code: [Select]

var
x: Single;
begin
x:= 1.8;
Writeln('My Car engine capacity is ', x, ' liters');
Writeln('Press enter key to close');
Readln;
end.the numbers are returned as:

Code: [Select]

My Car engine capacity is  1.799999952E+00 liters
Press enter key to close
I am using version 0.9.30.4-0 on Linux Mint 14

Any suggestions - please be gentle 

[idc65]

Hi

You could use the FloatToStrF function to format the output ie

Writeln('My Car engine capacity is '+FloatToStrF(x, ffFixed, 5, 3)+' liters');


the 5 is total length of formatted result, and the 3 is how many digits after the decimal place.

[barrydocks]

Thanks for the reply.

But what I Want to know is why the code didn't work as predicted?

Thanks

[idc65]

Floating-point accuracy loss can be the result of multiple causes:
If you assign a floating-point literal (for example: 0.1) to a floating-point variable, the floating-point variable might not have sufficient bits to hold the desired value without introducing some error. The floating-point literal might require a very large number or even an infinite number of bits for infinite precision representation.

More info can be found here, not all lazarus but the facts are the same.
a bit of light reading.
http://docwiki.embarcadero.com/RADStudio/XE4/en/Floating-Point_Rounding_Issues

[Leledumbo]

When you round 1.799999952E+00 to 1 number after decimal separator, it's 1.8.

[Rails]

Take a look at these:

http://en.wikipedia.org/wiki/Floating_point
http://floating-point-gui.de/

More than you ever wanted to know about floating point math and computers.   

[barrydocks]

Ok, Thanks.  Next question, why do I get this error:

Code: [Select]

project1.lpr(41,7) Error: Identifier not found "Format"
With this code:

Code: [Select]

var
Height: Double;
Weight: Double;
IdealWeight: Double;
begin
Write('What is your height in meters (e.g. 1.8 meter) : ');
Readln(Height);
Write('What is your weight in kilos : ');
Readln(Weight);
if Height >= 1.4 then
IdealWeight:= (Height - 1) * 100
else
IdealWeight:= Height * 20;if (Height < 0.4) or (Height > 2.5) or (Weight < 3) or
(Weight > 200) then
begin
Writeln('Invalid values');
Writeln('Please enter proper values');
end
else
if IdealWeight = Weight then
Writeln('Your weight is suitable')
else
if IdealWeight > Weight then
Writeln('You are under weight, you need more ',
Format('%.2f', [IdealWeight - Weight]), ' Kilos')
else
Writeln('You are over weight, you need to lose ',
Format('%.2f', [Weight - IdealWeight]), ' Kilos');
Write('Press enter key to close');
Readln;
end.
Thanks

[eny]

Ok, Thanks.  Next question, why do I get this error:

Because you can simply do:

Code: [Select]

Writeln('My Car engine capacity is ', x:5:2, ' liters');

(Or add 'sysutils' to your uses section...)

[barrydocks]

Ok, Thanks.  Next question, why do I get this error:

Because you can simply do:

Code: [Select]

Writeln('My Car engine capacity is ', x:5:2, ' liters');

(Or add 'sysutils' to your uses section...)

Ah-a, penny drops from a long way up!

Thanks