How do you add two fractions without user input in C++?

Question

I'm writing a program that solves fraction problems. The program inputs 26 fraction problems from a file (ex: 1/4 + 1/2) and stores them into an array. It then displays a random question from the array and should solve the problem and display the answer. I used getline to get each individual question from the file. How do I add the fractions together? I know how to add fractions in C++ but I just don't understand how to add them when it's inputted from a file, not user input.

EDIT: Here's my question. How do I add two fractions in a string? EX: "1/2 + 1/4"

This is my code so far:

#include <iostream>
#include <fstream>
#include <ctime>
#include <cstdlib>
#include <string>

using namespace std;

const int MAX = 50;

void loadProblems(string problems[], int &count);
int gcd(int a, int b);

int main()
{
    ifstream myFile;
    srand(static_cast<unsigned int>(time(0)));
    string problems[MAX];
    int count, mode, randomIndex;
    int n1, n2, n3, d1, d2, d3;
    char slash;

    cout << "Welcome to the Fraction Tutor V1 by Vince!\n\n" << endl;
    cout << "There are 5 problems per session. The computer will select a problem from a list of problems and you have up to three attempts per problem. You must provide answer in reduced form (i.e., enter 3/4 instead of 6/8)." << endl;
    cout << "Have fun and good luck.\n" << endl;

    cout << "Loading problems from the file ..." << endl;
    loadProblems(problems, count);

    cout << "There are " << count << " problems available\n" << endl;
    randomIndex = rand() % count;

    cout << "Available Modes" << endl;
    cout << "   1. Training mode" << endl;
    cout << "   2. Normal mode" << endl;
    cout << "Please select a mode: ";
    cin >> mode;
    cout << "\n";

    if (mode == 1)
    {
        cout << "Training mode is selected.\n" << endl;
        cout << "Computer is selecting a random problem ..." << endl;
        cout << problems[randomIndex] << endl;


    }
    if (mode == 2)
    {
        cout << "Normal mode is selected.\n" << endl;

    }

    return 0;
}

void loadProblems(string problems[], int &count)
{
    count = 0;
    string problem;
    ifstream myFile;
    myFile.open("P4Problems.txt");

    getline(myFile, problem);
    while (!myFile.eof())
    {
        problems[count] = problem;
        count++;
        getline(myFile, problem);
    }
}

Answer 1

If there's an idiomatic way to express rational numbers (aka integer fractions) using the C++ Standard Library, I haven't found it.

However this guy's written a useful class for storing fractions and doing mathematical operations on them: https://github.com/featdd/FractionClass

Featdd's Fraction even has a string constructor - if you can get the input down to "1/2" you're in business.

So you're left with reading a string, splitting it into "a/b", "+", "c/d" (where "+" could be any of the four main maths operations), and calculating the results.

I suggest you take a look at this earlier question for ideas on how to parse the string!

Answer 2

If I'm understanding your question correctly, you'll have to parse the string and break it down into its components. Assuming that your formatting above 1/4(space)+(space)1/2 is consistent, you could split the first fraction, the operation, and the second fraction into 3 strings (using the space as a delimiter). There is a good [OPINION] split function here that I have used before.

At this point you would have the following strings: "1/4", "+", "1/2". From here you could continue to break down the fractions (using the / as your delimiter), giving you numerator and denominators for both fractions.

Answer 3

I agree a parser (of any complexity) is probably not the simplest approach. Definately a good thing to learn ... but you first need to learn enough C++ to get at least a little progress.

Perhaps you might consider:

with input (at std::cin) :

1/4 + 1/2

your code needs to detect the integer 1 first in sequence.

Because this is a C++ question, a starting place for code to consider might be:

int n1 = 0;  // numerator of fraction 1

std::cin >> n1;
std::cout << "n1: " << n1 << std::endl; // during development, echo check

Next is the slash (numerator first)

char slash = 0;
std::cin >> slash;
std::cout << "slash: " << slash << std::endl;
assert(slash == '/');  // user entry error kills the program

Now the denominator:

std::cin >> d1; // denominator of fraction 1
std::cout << "d1: " << d1 << std::endl; // echo check

Now you have fraction 1 in two integer variables.

---

Do something similar to capture oper, n2, and d2.

Now with n1, d1, oper, n2, d2, do you think you can figure out how to proceed?

---

before you try too much more, it would be good for you to learn how to write a function. It appears you have several.

Might I suggest,

"void getFraction(int& n, int& d)"; // prompts user, gets two integers

Create this function, and see if you can read in f1 and echo it.

---

Now you can see that two un-associated ints will be inconvenient. So try, maybe

class Fraction;

which contains two integer, ctor, dtor.

Then move the getFraction() function into the class as "get()" Add method show() to class.

And proceed.

Good luck