C++ Input/output with files

Question

#include <iostream>
#include <fstream>

using namespace std;


int main()

{
    int a , b , c , d; 
    ifstream myfile;

    myfile.open ("numbers.txt");
    myfile >> a, b, c;
    d = a + b + c;

    ofstream myfile;
    myfile.open ("result.txt");
    myfile << d;
    myfile.close();

    return 0
}

The number.txt file contains 3 numbers 10 , 8 , 9. I am trying to get the program to read them and sum them up in the results.txt.

The errors I get are:

conflicting declaration 'std :: ifstream myfile'
no match for 'operator << in myfile << d'
'myfile' has a previous declaration as 'std :: ifstream myfile' 

Answer 1

(This only addresses one of the two errors in your code.)

myfile >> a, b, c;

This line doesn't read input to all three variables a, b, and c. It only reads input to a, then evaluates b and discards the value, then evaluates c and discards the value.

What you want is:

myfile >> a >> b >> c;

This will read a value to all three variables from myfile.

Answer 2

You cannot declare two different variables with the same name. You are first declaring myfile to be of type std::ifstream and then later you declare myfile to be of type std::ofstream. Name your output stream variable differently.