How do you add 2 decimal places to numbers? - c++

Question

This is my code. The information my professor gave us to only show 2 decimal points is out.precision(2) ;.
cout << "Welcome to the Book Store" << endl << endl;
cout << "Enter the single copy price: $" ;
cin >> single_copy_price ;
cout << "Enter the number of books sold: " ;
cin >> num_of_books_sold ;
cout << "Enter the discount percentage: " ;
cin >> discount_percentage ;
cout << "********************************************" << endl ;
subtotal = single_copy_price * num_of_books_sold ;
cout.precision(2) ;
cout<< "Subtotal: $" << subtotal << endl ;
cout << "Discount percentage: " << discount_percentage << "%" << endl ;
discount_ammount = subtotal * (discount_percentage / 100) ;
cout.precision(2) ;
cout << "Discount ammount: $ " << discount_ammount << endl ;
cout.precision(2) ;
cout << "Final price: $" << subtotal - discount_ammount << endl ;
return 0;
`
However, this is my result:
Welcome to the Book Store
Enter the single copy price: $10.50
Enter the number of books sold: 20
Enter the discount percentage: 15
Subtotal: $2.1e+02
Discount percentage: 15%
Discount ammount: $ 32
Final price: $1.8e+02
Program ended with exit code: 0
Thank you for the help!

Answer 1

The problem is the cout.setprecision(2). What it does is limit the number of significant figures in a number displayed. It's useful for scientific work, but not what you are looking for.
One person's solution was to write their own formatting method: http://www.arachnoid.com/cpptutor/student3.html
At the very end is point 6, for currency. His solution also formats with $ and commas for thousands places.
#include <iostream>
#include <iomanip>
#include <string>
using namespace std;
void showCurrency(double dv, int width = 14)
{
const string radix = ".";
const string thousands = ",";
const string unit = "$";
unsigned long v = (unsigned long) ((dv * 100.0) + .5);
string fmt,digit;
int i = -2;
do {
if(i == 0) {
fmt = radix + fmt;
}
if((i > 0) && (!(i % 3))) {
fmt = thousands + fmt;
}
digit = (v % 10) + '0';
fmt = digit + fmt;
v /= 10;
i++;
}
while((v) || (i < 1));
cout << unit << setw(width) << fmt.c_str() << endl;
}
The most simple solution is to set your precision to 2 more than the number of digits in the integer portion. To figure that out, cast to int and count the number of times you can divide by 10 with a non-zero result.