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Defined constants

 
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Defined constants
pietra
13 Mar, 2007 - 09:02 AM
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When constants are defined with #define, how do you know which type are they (int, long)? And do they have a type?

I have this code

CODE

#include <iostream>
#define PI 3.14159
int main ()
{
    
std::cout << PI;
getchar();
return 0;
}


output is

3.14159

And when I add more numbers for PI

CODE

#define PI 3.14159265


output is still

3.14159

Why is that?

This post has been edited by pietra: 13 Mar, 2007 - 09:08 AM
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Amadeus
RE: Defined Constants
13 Mar, 2007 - 09:09 AM
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It is important to remember that when using the define directive, it is actually implementing a macro that replaces any occurrences of the specified define (PI i this case) with the definition. It is a straight replacement in the code by the preprocessor. As such, there really are no data types for defines.
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pietra
RE: Defined Constants
13 Mar, 2007 - 09:17 AM
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Ok, no data types.

But why it won't display the whole number? Shouldn't it be a defined constant, how you -define- it it's up to you and how many digits there are is up to you as well? What if you need to use very precise calculation with let's say PI?
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Amadeus
RE: Defined Constants
13 Mar, 2007 - 09:23 AM
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Is it truncating or rounding? I'm afraid I'm not next to a compiler ATM...can you change #define PI 3.14159265 to #define PI 3.14159665 and see if it cuts or rounds?
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pietra
RE: Defined Constants
13 Mar, 2007 - 09:29 AM
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QUOTE(Amadeus @ 13 Mar, 2007 - 10:23 AM) *

Is it truncating or rounding? I'm afraid I'm not next to a compiler ATM...can you change #define PI 3.14159265 to #define PI 3.14159665 and see if it cuts or rounds?


I've change it and output is 3.1416

Sorry I don't get it
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Amadeus
RE: Defined Constants
13 Mar, 2007 - 09:31 AM
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That means that the number is being rounded somehow, not actually cut off.
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pietra
RE: Defined Constants
13 Mar, 2007 - 09:33 AM
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QUOTE(Amadeus @ 13 Mar, 2007 - 10:31 AM) *

That means that the number is being rounded somehow, not actually cut off.

Aha, I see. And that's suppose to be correct? Is this because of compiler or that's just the way it is? I use Dev C++ now.
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Xing
RE: Defined Constants
14 Mar, 2007 - 03:01 AM
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Include <iomanip> and add std::cout<<std::setprecision(10); before std::cout << PI;

This post has been edited by Xing: 14 Mar, 2007 - 03:02 AM
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AmitTheInfinity
RE: Defined Constants
14 Mar, 2007 - 05:25 AM
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QUOTE(Xing @ 14 Mar, 2007 - 04:31 PM) *

Include <iomanip> and add std::cout<<std::setprecision(10); before std::cout << PI;


yes xing is correct icon_up.gif . it's rounding it because it's precision for console out is 4 by default, so it round up the number if it does not fit into the format.[somewhat similar to C formating concepts]

so to get more precision or different format of output [hex, binary or only whole numbers etc.] we need to do formatting first using "iomanip" header file.
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pietra
RE: Defined Constants
15 Mar, 2007 - 01:26 AM
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And... it's working smile.gif

QUOTE(AmitTheInfinity @ 14 Mar, 2007 - 06:25 AM) *

it's rounding it because it's precision for console out is 4 by default

This was the missing fact.
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Xing
RE: Defined Constants
15 Mar, 2007 - 05:42 AM
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QUOTE(pietra @ 15 Mar, 2007 - 02:56 PM) *

And... it's working smile.gif

QUOTE(AmitTheInfinity @ 14 Mar, 2007 - 06:25 AM) *

it's rounding it because it's precision for console out is 4 by default

This was the missing fact.

I guess it's 6 instead of 4 not sure though.
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