decimal formatting

SterlingM · 11-08-2009, 05:34 PM

I have this function --

Code:

double Item::getPrice() {
	return (price + (price * 0.07)).digits(2);
}

First of all, is digits(int) the correct way to format decimals (I only want two digits to the right of the decimal)? The compiler says I need a struct/class/union to the left of digits(). I'm not sure what I would use for that..

nadroj · 11-08-2009, 10:26 PM

No. Did someone suggest you do it this way?

Also, the computer doesnt care how many decimal places there are, either should you. However, you only really need to worry about this sort of thing when you are doing output, ex "cout" to the screen. So this function should just return the result, then whatever function is responsible for the output should worry about how it should be printed. Check this link out, which has examples at the bottom: setprecision - C++ Reference

SterlingM · 11-09-2009, 01:13 AM

Code:

	Beverage coke("coke", 3.65, false);
	cout<<setprecision(3)<<coke.toString();

No matter what I change the setprecision parameter to, it always displays 3.9055. Is it because I am calling a function? toString() looks like this.

Code:

string Beverage::toString() {
	ostringstream result;
	if(isAlcoholic == true)
		result<<getName()<<" is an alcoholic beverage."<<std::endl;
	else
		result<<getName()<<" is an non-alcoholic beverage."<<std::endl;
	result<<"It's price is "<<getPrice()<<"."<<std::endl;
	return result.str();
}

**laserlight** · 11-09-2009, 01:18 AM

You should use setprecision within the toString() member function. By the way, have you considered overloading operator<< for std::ostream instead of writing a toString() member function?

SterlingM · 11-09-2009, 01:33 AM

Okay I got that. If I wanted it in "##.##" form, what can I use to do that? Does precision handle that? Or is there some other way to do it?

**laserlight** · 11-09-2009, 01:42 AM

You could use std::setw with std::setfill. Frankly though, this kind of formatting is not one of the strong points of C++'s output streams; C's formatted output functionality probably does this better. You can get similiar printf-like functionality for C++ output streams via Boost.Format.

11-08-2009, 05:34 PM	#1
SterlingM Registered User Join Date: Oct 2009 Posts: 38	decimal formatting I have this function -- Code: double Item::getPrice() { return (price + (price * 0.07)).digits(2); } First of all, is digits(int) the correct way to format decimals (I only want two digits to the right of the decimal)? The compiler says I need a struct/class/union to the left of digits(). I'm not sure what I would use for that..
SterlingM is offline

11-08-2009, 10:26 PM	#2
nadroj Registered User Join Date: Oct 2006 Location: Canada Posts: 848	No. Did someone suggest you do it this way? Also, the computer doesnt care how many decimal places there are, either should you. However, you only really need to worry about this sort of thing when you are doing output, ex "cout" to the screen. So this function should just return the result, then whatever function is responsible for the output should worry about how it should be printed. Check this link out, which has examples at the bottom: setprecision - C++ Reference
nadroj is offline

11-09-2009, 01:18 AM	#4
laserlight C++ Witch Join Date: Oct 2003 Location: Singapore Posts: 10,368	You should use setprecision within the toString() member function. By the way, have you considered overloading operator<< for std::ostream instead of writing a toString() member function? __________________ C + C++ Compiler: MinGW port of GCC Build + Version Control System: SCons + Bazaar Look up a C/C++ Reference and learn How To Ask Questions The Smart Way
laserlight is offline

11-09-2009, 01:33 AM	#5
SterlingM Registered User Join Date: Oct 2009 Posts: 38	Okay I got that. If I wanted it in "##.##" form, what can I use to do that? Does precision handle that? Or is there some other way to do it?
SterlingM is offline

11-09-2009, 01:42 AM	#6
laserlight C++ Witch Join Date: Oct 2003 Location: Singapore Posts: 10,368	You could use std::setw with std::setfill. Frankly though, this kind of formatting is not one of the strong points of C++'s output streams; C's formatted output functionality probably does this better. You can get similiar printf-like functionality for C++ output streams via Boost.Format. __________________ C + C++ Compiler: MinGW port of GCC Build + Version Control System: SCons + Bazaar Look up a C/C++ Reference and learn How To Ask Questions The Smart Way Last edited by laserlight; 11-09-2009 at 01:45 AM.
laserlight is offline

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
return decimal number back caller function	andy09	C Programming	7	10-10-2009 08:10 AM
hex to binary,hex to decimal	groovy	C Programming	2	01-25-2006 02:14 AM
Confused by expression.	Hulag	C Programming	3	04-07-2005 07:52 AM
dos game help	kwm32	Game Programming	7	03-28-2004 06:28 PM