Multiplying elements in array not working in c++? - c++

Question

I am trying to make a simple program in c++ that takes the price and number of items purchases, stores it in arrays, and then outputs the totals for each item in a tabular format. However, when I multiply the numbers in my code, I get totally strange answers! Can someone please enlighten me as to what's going on?
Code:
#include <iostream>
using namespace std;
int main(int argc, _TCHAR* argv[]) {
float price[4], tot[4];
int amt[4];
cout << "Please enter the price and amount of 4 items:\n";
for (int i = 0; i<4; i++) {
cout << "Price of item " << i + 1 << ": ";
cin >> price[i];
cout << "Amount of item " << i + 1 << ": ";
cin >> amt[i];
if (price[i] <= 0 || amt[i] <= 0) {
cout << "Invalid Input Entry!\n";
break;
}
tot[i] = price[i] * amt[i]; // I can't really see how I could have messed this up...
}
cout << "Total\t\tPrice\t\tAmount\n";
cout << "-----\t\t-----\t\t------\n";
for (int i = 0; i < 4; i++) {
cout << "$" << fixed << cout.precision(2) << tot[i] << "\t\t$" << price[i] << "\t\t" << amt[i] << endl;
}
system("pause");
return 0;
}
Output:

Answer 1

The problem is that you are outputting the return value of cout.precision(2) (which returns the previous precision, in this case 6 initially and then 2 afterwards) in front of each total price.
You need to either:
not pass the return value of cout.precision() to operator<<:
cout << "$" << fixed;
cout.precision(2);
cout << tot[i] << ...
or, call precision() one time before entering the loop:
cout.precision(2);
for (int i = 0; i < 4; i++) {
cout << "$" << fixed << tot[i] << "\t\t$" << price[i] << "\t\t" << amt[i] << endl;
}
use the std::setprecision() stream manipulator instead of calling cout.precision() directly:
#include <iomanip>
for (int i = 0; i < 4; i++) {
cout << "$" << fixed << setprecision(2) << tot[i] << "\t\t$" << price[i] << "\t\t" << amt[i] << endl;
}
or
#include <iomanip>
cout << setprecision(2);
for (int i = 0; i < 4; i++) {
cout << "$" << fixed << tot[i] << "\t\t$" << price[i] << "\t\t" << amt[i] << endl;
}
On a side note, you should not use \t characters to control the formatting of your table. Use stream manipulators like std::setw(), std::left, etc instead:
#include <iostream>
#include <sstream>
#include <iomanip>
#include <cstdlib>
using namespace std;
const int maxItems = 4;
string moneyStr(float amount)
{
ostringstream oss;
// in C++11 and later, you can replace this with std::put_money() instead:
// http://en.cppreference.com/w/cpp/io/manip/put_money
//
// oss << showbase << put_money(amount);
oss << "$" << fixed << setprecision(2) << amount;
return oss.str();
}
int main(int argc, _TCHAR* argv[])
{
float price[maxItems], tot[maxItems];
int amt[maxItems];
int cnt = 0;
cout << "Please enter the price and amount of " << maxItems << " items:" << endl;
for (int i = 0; i < maxItems; ++i)
{
cout << "Price of item " << i + 1 << ": ";
cin >> price[i];
cout << "Amount of item " << i + 1 << ": ";
cin >> amt[i];
if (price[i] <= 0 || amt[i] <= 0) {
cout << "Invalid Input Entry!" << endl;
break;
}
tot[i] = price[i] * amt[i];
++cnt;
}
cout << left << setfill(' ');
cout << setw(16) << "Total" << setw(16) << "Price" << setw(16) << "Amount" << endl;
cout << setw(16) << "-----" << setw(16) << "-----" << setw(16) << "------" << endl;
for (int i = 0; i < cnt; i++) {
cout << setw(16) << moneyStr(tot[i]) << setw(16) << moneyStr(price[i]) << setw(16) << amt[i] << endl;
}
system("pause");
return 0;
}
Live Demo