How to set a result to 2 decimal places

[Noobiez]

I'm only allowed to use the <iostream> library, so setprecision can't be used. How can I set 2 decimal places for the average?

  average = sum/(double)n;
    cout << "Average = "<<average << endl;

[jonnin]

int ipart = (int)(average * 100);
average = ipart / 100.0;

//now has 2 decimal places. but it will still print zeros. If you want to get rid of the zeros you can either

convert it to text and take a substring, find the decimal point and take 2 more characters.

or do a messy decimal to 2 integer + custom print statement (let me know if you want this one).

I thought fmod might offer a cool answer but maybe not (anyone?).

also try this gem:
cout << average << "\b\b\b" << " " << endl; //back up 3 characters and overwrite with 3 spaces...

[Duthomhas]

Er,

1 2 3 4

double pi = 3.1415926; std::cout << "whole part: " << (int)pi << "\n"; std::cout << "fractional part: " << (int)((pi - (int)pi) * 100) << "\n";

while part: 3 fractional part: 14

Make yourself a function.

#include <iostream>

std::ostream& print( std::ostream& outs, double x )
{
  return outs
    << (int)x << "."
    << (int)((x - (int)x) * 100);
}

int main()
{
  double pi = 3.1415926;
  print( std::cout, pi ) << "\n";
}

Write your own manipulator.

#include <iostream>

struct myprec2
{
  double x;
  myprec2( double x ): x(x) { }
};

std::ostream& operator << ( std::ostream& outs, const myprec2& p )
{
  return outs
    << (int)p.x << "."
    << (int)((p.x - (int)p.x) * 100);
}

int main()
{
  double pi = 3.1415926;
  std::cout << myprec2( pi ) << "\n";
}

Etc.
[edit]
I forgot something important -- leading zeros. See below.

[jonnin]

I started to do a simpler version of that but
100.01
becomes
100 and 1 integer parts
and prints 100.1

so you have to handle that aggravation.
I think all you need is
if ( (int)val - val < 10)
cout <<'0' ; //insert extra zero padding.

[Duthomhas]

LOL, you're right. (I was half asleep when I wrote that above.)

int frac = (x - (int)x) * 100;

std::cout << (int)x;
if (frac < 10) std::cout << "0";
std::cout << frac;

Thanks jonnin!