How to round a double value

[King_of_Queens]

Hi i search for a function which can do this: double value = 4,6793 value = round(value,2) //after that value should be 4,68 in which library can i find this function???

[Lost User]

do you mean round to 4,6800? or truncate to 467.93 and round to 468? I don't really get how you can get 4,68? You'll need to make you own round routine though if you want to do anything really weird with numbers

[King_of_Queens]

Hi i mean this: round(y,x) y = value to round for example 4,6793233 x = position after ',' to round round should look after y at position x+1 if y at positon x is > 5 then 4,68 forget the rest of numbers!

[Lost User]

OK, I'm not aware of any function in the standard libs that'll do what you want. Also, if the number you specify is a double where does this comma come from? I mean the double number 46793233 would be 46,793,233. So I'm assuming the comma is always after the first digit? Either way, iterating through figures is a bit of a nightmare, and i'm not really sure of the best way to go about it, sorry.

[vcplusplus]

In some countries they use the ',' intead of the '.'. Example: In America 4.67 In Italy 4,67

[David Crow]

This should work for you: double a = 4.6793; a = a + 0.005; // 4.6843 int b = a * 100.0; // 468 double c = b / 100.0; // 4.68

[Lost User]

Interesting...why is that? The '.' is a decimal point to indicate decimal figures in a number, so why use a ','? :confused: Cheers for pointing that out to me though, I would never have guessed :)

[Lost User]

Now I know what I'm doing, I'd do it like this : //could make it a variable parameter so you don't have to keep supplying //it with a param when you just want a standard round. double rounddouble(double val, int fig=0) { //Avoid division by zero by checking fig for zero if(fig != 0) { //get the multiply divide factor double sigfig = pow(10, (double)fig); //multiply the figure by 10pow to get the pos to chop the end off val *= sigfig; //add 0.5 before rounding so we round up or down val += 0.5; //adding 0.5 affects round down value in effect, rounding up or down. val = floor(val); //return the decimal to original value with chopped off rounded crap val /= sigfig; } else { //just round the figure without an offset val += 0.5; val = floor(val); } //finally return the value return val; } Hope this helps. This will return the correct rounded double value based on however many significant fig's you specify. Alan.;P

[QuiJohn]

Dangleberry wrote: Interesting...why is that? The '.' is a decimal point to indicate decimal figures in a number, so why use a ','? Because it's the other way around in a lot of countries. :) It can throw you at first, but it's something to keep in mind while on international forums.

[vcplusplus]

A decimal point is an English notation. Most other countries use decimal commas, and the thousand separator is a period.

[ohadp]

I think this short scribble should work: double round(double x, int digits) { double _int = (double)((int)x); double _pow = pow(10, digits); double _fract = (x - _int) * _pow; return _int + (_fract / _pow); }