Thread: Finding Ratio of Two Variables Input by User

Originally Posted by Osman Zakir

So would writing an if-condition to check (number_of_cents >= 100) be good? And if so, and I need a for-loop, how should I have it put the decimal points at the right spot?

No, think about it: if I gave you 123 cents, how many dollars would you have? How would you calculate it?

And is this good so far?

Looks good for an initial attempt.

Or should I wrap the '1' in quotes (if so, then single or double?)?

Quotes are for characters. '1' means the character 1, not the number 1. Double quotes are for (C-style) strings, which is just an array of characters with a \0 at the end, so "1" is just '1' and '\0'. Since your money is of integral type, you should compare with...?

And is the approach good so far, or am I messing up in a huge way here?

The approach is good so far. It can be simplified later perhaps, due to repetition of much code, but that's for later.

By the way, anybody of a good, free, Web-based VPN service? Or just a good way to configure OpenVPN with a free account so that I can use my credentials and successfully connect to it?

Probably should just ask this separately in the techtalk forum.

Edit: How should I calculate the number of coins, though? I mean, like, how do I make the program correctly calculate the values of the coins and add them such that it prints out the correct value in dollars and cents?

How would you do it in real life? Pick an example (that is, make up some number of each coin) and write it down in simple steps how you do it.

Well, I don't see anywhere in the exercise that you should only input cents and converts that to the different coins. I only see that you should enter the different coin amounts, convert it to cents and dollars.

>>If you gave me 123 cents, that'd mean you gave me $1.23
So how did you get $1.23?

So for the reverse, think about this: if a product cost $0.99 and you pay $2, how do you figure out how much exchange to give back, and how many of each coin?

The exercise is specifically about asking the user for input, not encoding it into an array. Besides, this array approach, while more compact, reduces readability.

Educational it certainly is. But what index of the array is nickels? Dimes? Pennies? Hard to know. Hard to read.

^Exactly. I do want to know of a good looping technique I can use where I don't have to hard-code it so much, but really, I'd like to be able to read the code and know what variable is for which type of coin and which value is being given to which coin.

It certainly would be good if I could make it more simple and efficient. Stroustrup keeps repeating in his book that code should be correct, simple, and efficient (the importance of each is seen by the order in which they each are listed, by the way, so correctness is most important -- he also said that it doesn't matter if a program is really fast if its output is incorrect, and also that code shouldn't be complicated). If the program's execution time could be reduced, that'd be great.

Edit: About that calculator program I mentioned; it'd still be good if somebody help me make it more simple and efficient, but for now I've at least got the loop to work:

Code:

#include <iostream>

using namespace std;

double calculator(string operation, double first_value, double second_value);

int main()
{
    char answer;
    cout << "< -- Mini Calculator Program -- >\n";
    cout << "Please provide operation (+, -, /, *): ";
    string operation;
    cin >> operation;
    cin.ignore();
    double first_value;
    double second_value;
    cout << "Please enter the first value: ";
    cin >> first_value;
    cin.ignore();
    cout << "Please enter the second value: ";
    cin >> second_value;
    cin.ignore();
    double result = calculator(operation, first_value, second_value);
    cout << "The result of your calculation is: " << result << ".\n";
    cout << "Would you like to continue (Y/N)?\n";
    cin >> answer;
    cin.ignore();
    if (answer == 'Y' || answer == 'y')
    {
        while (answer == 'Y' || answer == 'y')
        {
            cout << "Please provide operation (+, -, /, *): ";
            cin >> operation;
            cin.ignore();
            cout << "Please enter the first value: ";
            cin >> first_value;
            cin.ignore();
            cout << "Please enter the second value: ";
            cin >> second_value;
            cin.ignore();
            result = calculator(operation, first_value, second_value);
            cout << "The result of your calculation is: " << result << ".\n";
            cout << "Would you like to continue (Y/N)?\n";
            cin >> answer;
            cin.ignore();
            if (answer == 'N' || answer == 'n')
            {
                cout << "Very well. Thanks for using this calculator program.\nQuitting . . . \n";
                return 0;
            }
        }
    }
    else if (answer == 'N' || answer == 'n')
    {
        cout << "Very well. Thanks for using this calculator program.\nQuitting . . . \n";
        return 0;
    }
    else
    {
        cout << "That's not Y or N!\n";
        return 0;
    }
    cin.ignore();
}

double calculator(string operation, double first_value, double second_value)
{
    double result;
    if (operation == "+")
    {
        result = first_value + second_value;
    }
    else if (operation == "-")
    {
        result = first_value - second_value;
    }
    else if (operation == "/")
    {
        result = first_value / second_value;
    }
    else if (operation == "*")
    {
        result = first_value * second_value;
    }
    return result;
}

What if you had 20 currency units instead of 5? want 20 variables and 4 screens of text to wade through to find a typo or debug other things?

Plus if you're smart with design it doesn't matter that you know which variable corresponds to which coin. You can do a loop for getting input using both the string array and the integer array. That way the output is always linked to the input, even if you change the order of dimes/nickels etc. You don't even need to read the string array. Though you'd have to modify calculate money slightly to cope with the flexibility.

As for your calculator, again you have code repetition, so try to only use the loop. I actually did this exercise I think, long time ago. Here's the code I had back then:

Code:

#include <iostream>
#include <string>
#include <cctype>
#include <cstdlib> //atoi, because std::stoi isn't an option :-), same goes for atof
#include <sstream> //for custom stoi function, std::stoi doesn't work with windows g++
#include <limits> //numeric_limits for flushing cin buffer


using std::cout;
using std::endl;
using std::cin;


float multiply(float x, float y)
{    return x*y;}
float divide(float x, float y)
{    return x/y;}
float add(float x, float y)
{    return x+y;}
float subtract(float x, float y)
{    return x-y;}


int stoi(const std::string& s) { //deprecated, using floats now
    std::istringstream str(s);
    int i;
    str >> i;
    return i;
}


float stof(const std::string& s) {
    std::istringstream str(s);
    float i;
    str >> i;
    return i;
}


bool nondigit(const std::string& s) //true if s contains a non-digit other than a single '.' or starting '-'
{
  bool b = false;
  int dotcnt = 0; //for floats
  int i = 0;
  auto msg = [&]() { cout<<"!!"<<s[i]<<"!!\n"<<"Invalid number, retry please"<<endl; };


  for (i;i<s.length();i++)
  {
    if (std::isdigit(s[i])) {/*keep going*/}
    else if (s[i]=='.') {
        if(dotcnt==0){++dotcnt;}
        else{msg(); b = true; break;}
    }
    else if (s[i]=='-'){
      if(i>0){msg(); b = true; break;}//minus not at front: exit
    }
    else {msg(); b=true; break;}
  }
  return b;
}




void getinput(float &x, float &y) //parses getlines
{
    std::string xstr;
    std::string ystr;
    cout<<"Enter x (left operand)"<<endl;


    do{
    getline(cin,xstr);
    }while ((xstr.length()==0) || (nondigit(xstr)));


    x = stof(xstr); //version 1
    cout<<"Enter y (right operand)"<<endl;


    do{
    getline(cin,ystr);
    }while((ystr.length()==0) || (nondigit(ystr)));


    y = atof(ystr.c_str()); //version 2
}


void promptuser(char &op) //cin<< char with input checking
{
    cout<<"What operation would you like to perform?: add(+),subtract(-), divide(/), multiply(*), exit(e)";
    do
    {
      cin.get(op);
      if (cin.fail())
      {
      cout<<"How'd you break it?"<<endl;
      cin.clear();
      }
    cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
    if ((op=='e')||(op=='+')||(op=='-')||(op=='*')||(op=='/')){break;}
    else {cout<<"Wrong input, try again (case sensitive)"<<endl;}
    }while(true);
}




int main()
{
char op {}; //operator input
float x,y;


    while(op!='e')
    {
    promptuser(op);
    if (op!='e')
    {
        getinput(x,y);
        switch(op)
        {
        case '+':
         cout<<x<<"+"<<y<<"="<<add(x,y)<<endl;         break;
        case '-':
         cout<<x<<"-"<<y<<"="<<subtract(x, y)<<endl;         break;
        case '/':
         cout<<x<<"/"<<y<<"="<<divide(x, y)<<endl;         break;
        case '*':
         cout<<x<<"*"<<y<<"="<<multiply(x, y)<<endl;         break;
         default: throw "somehow you managed to enter something weird for op";
        }
    }
    else
    {
        cout<<"Shutting down...";
    }
    }




    return 0;
}

How would you write them in real life? If I gave you 123, how'd you write it with words?