Reading in from a file

[DanStirletz]

Please do not post links to read in writing into a file tutorials here. I already read them, and did not find an answer.

I wrote a program that reads values for Rate and L from a file. However i do not know how to properly write the file for reading-in in the first place, and it gives me an infinite loop.

Here is the file content:

Rate= 0.25;
L=540;
Rate = 0

Here is the program code:

#include <iostream>
#include <fstream>
#include <cmath>
using namespace std;



int main()

{

ifstream infile("coolfile.dat");
double Rate, L, N, Payment;

N = 12;

infile >> Rate >> L;

while(Rate>0){

Payment = ((Rate * pow((1+Rate),N))/(pow((1+Rate),N) - 1)) * L;

cout << "For " << N << " payments of a loan of " << L << " the monthly payment is " << Payment << endl;

}
infile.close();
return 0;
}


Thank you for your help.

[DanStirletz]

bump

[Chervil]

If this is the exact contents of the file:

Rate= 0.25;
L=540;
Rate = 0

then I'd recommend reading each line into a string, using the getline() function.
Then either use a stringstream to parse the data, or use the string functions to find the '=' sign, and split the string accordingly into subtrings. If you use the latter option, you may still need to convert the string into a number, for example using strtod().
The stringstream approach is probably easier.

#include <iostream>
#include <string>
#include <sstream>
#include <iomanip>

using namespace std;

int main()
{
    string data= "Rate= 0.25;\nL=540;\nRate = 0";
    istringstream infile(data);
    
    string line;
    while (getline(infile, line))
    {
    	istringstream ss(line);
    	string name;
    	double number = 0.0;
    	getline(ss,name,'=');
    	ss >> number;
    	cout << "Name: " << setw(6) << left << name 
		     << " Number: " << number << endl;    	
    }

    return 0;
}

Name: Rate   Number: 0.25
Name: L      Number: 540
Name: Rate   Number: 0

Lines 10 and 11 are just for this demo, you should use the normal disk file, but the behaviour should be the same in the rest of the code.