Question

(a) Write a function in C++ called readNumbers() to read data into an array from a file. Function should have the following parameters:

(1) a reference to an ifstream object

(2) the number of rows in the file

(3) a pointer to an array of doubles

The function returns the number of values read into the array. It stops reading if it encounters a negative number or if the number of rows is exceeded.

(b) Write a program with the main() function is designed to use the readNumbers() function from the previous part of this question to read the data from a file called inputData.txt to the array.

Answer 1

The following C++ program does all the required tasks:(Read the comments). The number of rows to be read from the file is passed to the function.

#include <iostream>
#include <fstream>

using namespace std;
//The required function
int read_numbers(ifstream &f, int r, double *p) {
    int i=0;
    //To read each double
    double x=0.0;
    while(i<r) {
        //if the file exhausts
        if(!(f >> x)) break;
        //for negative numbers 
        if(x<0) break;
        //read the number into array
        p[i] = x;
        //increment i
        i++;
    }
    return i;
}
int main()
{
    ifstream f1;
    f1.open("inputData.txt");
    //rows to be read from the file
    // this can be calculated as well from the file
    int rows = 6;
    double p[rows];
    int nums = read_numbers(f1, rows, p);
    cout << nums << endl;
    f1.close();
}

Create an input file -- inputData.txt (in the same folder as the above cpp program)

3.5
4.7
6
56
-1
76

Output:

4

As 4 lines are read successfully into the array. The 5th line contains a negative number and the loop breaks at this line.

Note(Optional):- The number of lines in the file can also be precalculated in main() if required:

double x=0.0;

int rows  = 0;

while(f1>>x) rows++;

//but then clear  the state and move f1 again to the start of the file

f1.clear();

f1.seekg(0);