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Join Date: Apr 2009

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Akis2000

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round

May 8th, 2009

hello, i have a double value=0;

and i want before starting the calulation to round this value
in the numbers that the user add, for example 2...

any ideas??? I have despered...........

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tux4life

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Re: round

May 8th, 2009

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Originally Posted by Akis2000

hello, i have a double value=0;

and i want before starting the calulation to round this value
in the numbers that the user add, for example 2...

any ideas??? I have despered...........

I don't understand that, can you give an example ?

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ShawnCplus ShawnCplus is offline

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Re: round

May 8th, 2009

With the math.h (or cmath someone correct me on this) header you can use the floor and ceil functions if I remember correctly to round down and round up respectively.

Last edited by ShawnCplus; May 8th, 2009 at 3:59 pm.

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Akis2000

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Re: round

May 8th, 2009

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
double pi1=0;
 
for (int long n=1; n<=10000; n++) 
{//star for loop
	 pi1 += (4*pow(-1.0, n+1))/(2*n - 1); 
}//end loop
double pi1=0;

for (int long n=1; n<=10000; n++) 
{//star for loop
	 pi1 += (4*pow(-1.0, n+1))/(2*n - 1); 
}//end loop

before loop for i want the pi1 round=number by the user...
for example user give 3 the pi1 =3.140

Last edited by Akis2000; May 8th, 2009 at 4:04 pm.

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tux4life

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Re: round

May 8th, 2009

•

Originally Posted by Akis2000

Help with Code Tags

C++ Syntax (Toggle Plain Text)
double pi1=0;
 
for (int long n=1; n<=10000; n++) 
{//star for loop
	 pi1 += (4*pow(-1.0, n+1))/(2*n - 1); 
}//end loop
double pi1=0; for (int long n=1; n<=10000; n++) {//star for loop pi1 += (4*pow(-1.0, n+1))/(2*n - 1); }//end loop
before loop for i want the pi1 round=number by the user...
for example user give 3 the pi1 =3.140

I actually wanted to see an example with concrete numbers, and as already mentioned: the floor and ceil functions from the C++ math library perform rounding on numbers

(and oh, if you post a snippet of code, could you please post it using code tags then ?)

Last edited by tux4life; May 8th, 2009 at 4:11 pm.

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tux4life

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Re: round

May 8th, 2009

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Originally Posted by ShawnCplus

With the math.h (or cmath someone correct me on this) header you can use the floor and ceil functions if I remember correctly to round down and round up respectively.

In C++ cmath is the preferred way, use math.h only if your compiler doesn't support the new header file style (e.g.: cmath ), but the use of math.h is not wrong

Last edited by tux4life; May 8th, 2009 at 4:10 pm.

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Akis2000

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Re: round

May 8th, 2009

ok i have this... but i have overloaded... error with pow...

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
ceil(pi1 * pow( 10,digits ) - 0.5) /pow(10,digits);
ceil(pi1 * pow( 10,digits ) - 0.5) /pow(10,digits);

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tux4life

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Re: round

May 8th, 2009

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Originally Posted by Akis2000

ok i have this... but i have overloaded... error with pow...
Help with Code Tags

C++ Syntax (Toggle Plain Text)
ceil(pi1 * pow( 10,digits ) - 0.5) /pow(10,digits);
ceil(pi1 * pow( 10,digits ) - 0.5) /pow(10,digits);

If you're having an error, can you please mention it also, so we can take a look at it?

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NathanOliver NathanOliver is offline

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Re: round

May 8th, 2009

if you mean that you want to round the number to a specific number of decimal places you might want to make a char array and use _gcvt() to store in the number of digits you want. for your example if you want pi to 5 places you could do this.

 Help with Code Tags 
 c++ Syntax (Toggle Plain Text) 
const double fullPi=3.141592653589793;
char * pi = new char[8];
_gcvt(fullPi, 8, pi);
const double fullPi=3.141592653589793;
char * pi = new char[8];
_gcvt(fullPi, 8, pi);

_gcvt() takes in a double and outputs the number of digits specified in the second term then it outputs the string into the char[] in the third term. for this you need to have an array that is big enough to hold the digits before the decimal place the decimal itself the number of digits after the decimal point and the terminating null at the end so in this case for 5 places you need a char[] of size 8.

Last edited by NathanOliver; May 8th, 2009 at 7:40 pm.

if you write using namespace std; you do not need to write std::something in your program.
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Akis2000

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Re: round

#10

May 8th, 2009

yeup, this is correct, but if i want to round a value before i calculate the value???

for example, i have value pi1: and i want to round this value before i go to the calculation.......

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
double pi1=0;
//here i want a code that tell to the for loop that the pi1 is 
only 2 digits.... ( the user select the number )  3.14 it's example
for (int long n=1; n<=10000; n++) 
{
	 pi1+= (4*pow(-1.0, n+1))/(2*n - 1);
}
 
double pi1=0;
//here i want a code that tell to the for loop that the pi1 is 
only 2 digits.... ( the user select the number )  3.14 it's example
for (int long n=1; n<=10000; n++) 
{
	 pi1+= (4*pow(-1.0, n+1))/(2*n - 1);
}