2

I'm new to the getline function in C++.

I'm writing a simple program that creates a struct for a Fraction, which reads in a numerator and denominator. Then, I'm writing a void printFraction() function which takes in the struct as a parameter and outputs the numerator divided by the denominator.

However, I'm getting an error that says that there is no matching function for getline, and that it requires arguments but is only getting 2. How can I find what the problem is?

#include <iostream>
using namespace std;

struct Fraction {
    int numerator;
    int denominator;
};

void printFraction(Fraction f);
int main() {
    Fraction f;
    cout << "Please enter numerator";
    getline(cin, f.numerator);
    cout << "Please enter denominator";
    getline(cin, f.denominator);
    cin.ignore();
    printFraction(f);
}

void printFraction(Fraction f) {
    cout << f.numerator << "/" << f.denominator;
}
halfer
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Andrew
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    `getline` is for getting a whole input line as a string, not as `int`. If you want formatted input use `cin >>`, e.g. `cin >> f.numerator;` – user17732522 Mar 01 '22 at 07:15

3 Answers3

6

First thing, you must include string:

#include <string>

Also, getline doesn't work with int. So you'll have to take in a std::string and then convert that string into int.

Consider not using the following in your code:

using namespace std;

..as it's considered as bad practice. For more info on why, look up to why is "using namespace std" considered as a bad practice.

So after all these fixes, here's the final code:

Final Code:

#include <iostream>
#include <string>

struct Fraction {

    int numerator;
    int denominator;
};

void printFraction(Fraction f);

int main() {

    Fraction f;
    std::string numerator, denominator;

    std::cout << "Please enter numerator: ";
    std::getline(std::cin, numerator);

    std::cout << "Please enter denominator: ";
    std::getline(std::cin, denominator);

    f.numerator = std::stoi(numerator);
    f.denominator = std::stoi(denominator);

    printFraction(f);
}

void printFraction(Fraction f) {

    std::cout << f.numerator << '/' << f.denominator;
}
The Coding Fox
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3

So, you can't use getline on an integer int, it reads the entire line as a string. Therefore you can either use std::cin for input or convert your line into an integer by doing the following

#include <iostream>
#include <string>

using namespace std;    
 
struct Fraction {    
        int numerator;
        int denominator;
};    

void printFraction(Fraction f);    

int main() {    
        Fraction f;
        string line;

        cout << "Please enter numerator";
        getline(cin, line);
        f.numerator = stoi(line); // stoi() converts a string to an integer

        cout << "Please enter denominator";
        getline(cin, line);
        f.denominator = stoi(line);
        cin.ignore();

        printFraction(f);
 
}    
 
void printFraction(Fraction f) {    
        cout << f.numerator << "/" << f.denominator;
}
kerolloz
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Dusan Todorovic
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0

Problem

First of all include the string library

#include <string>

secondly getline is used to read inputs in string format hence the error and third don't using namespace std; it is considered a bad programming practice.

Solution

After obtaining the user input in string format use stoi to convert the variable to an integer that will enable you to perform arithmetic operations

I have modified your code down below

#include <iostream>
#include <string>

   
struct Fraction {
    int numerator;
    int denominator;
};

void printFraction(Fraction f);


int main() {
    Fraction f;
    std::string numerator, denominator;

    std::cout << "Please enter numerator";
    std::getline(cin, numerator);

    std::cout << "Please enter denominator";
    std::getline(cin, denominator);

    f.numerator = std::stoi(numerator);
    f.denominator = std::stoi(denominator);

    printFraction(f);
}

void printFraction(Fraction f) {
    std::cout << f.numerator << "/" << f.denominator;
}

References

stoi() C++

getline() C++

Ammar
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