Reading data from text file - C++

Question

josey_matt 0 Newbie Poster

16 Years Ago

Hi, could anybody please tell me what i am doing wrong in this program.

The goal is to read the student name and grade from a text file and print it on the screen.

This is what i have so far. by the way this is for a school project that is due this coming Monday. The attached file is the input source.

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

//void calculateAverage();
//int calculateGrade();
//void updateFrequency();

int main()
{
	const int size=10;
	int debug=size;

	int test1[size], test2[size], test3[size], test4[size], test5[size];
	ifstream infile;
	for(int i=0;i<size;i++)
	{
		test1[i]=0;
		test2[i]=0;
		test3[i]=0;
		test4[i]=0;
		test5[i]=0;
	}

	cout<<"Reading from file ''input.txt''..."<<endl;
	infile.open("input.txt");

	while(size==debug)
	{
		for(int i=0;i<size;i++)
		{
			infile>>test1[i];
			infile>>test2[i];
			infile>>test3[i];
			infile>>test4[i];
			infile>>test5[i];
		}
		debug--;
	}
	
	for(int i=0;i<size;i++)
	{
		cout<<test1[i]<<" "<<test2[i]<<" "<<test3[i]<<" "<<test4[i]<<" "<<test5[i]<<" "<<endl;
	}
	infile.close();
	system("pause");
	return 0;
}

c++ school-education

input.txt (0.23 KB)

Josey 85 83 77 91 76
Johnson 85 83 77 91 76 
Aniston 80 90 95 93 48 
Cooper 78 81 11 90 73 
Gupta 92 83 30 69 87 
Blair 23 45 96 38 59 
Clark 60 85 45 39 67 
Kennedy 77 31 52 74 83 
Bronson 93 94 89 77 97 
Sunny 79 85 28 93 82

4 Contributors
4 Replies
8K Views
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Latest Post 13 Years Ago Latest Post by siddiquedu

Dani AI

Generated 11 Months Ago

Common pitfalls here are (1) extracting integers when the record begins with a name (the first extraction fails and leaves your arrays unchanged at 0), and (2) not checking the stream state after each read. A simple, robust pattern is to read each line, then parse it into a name plus grades. Use double if you expect fractional grades.

#include <fstream>
#include <sstream>
#include <vector>
#include <array>
#include <string>
#include <iostream>
using namespace std;

struct Student { string name; array<double,5> scores; };

int main() {
    ifstream in("input.txt");
    if (!in) { cerr << "Unable to open input.txt\n"; return 1; }

    vector<Student> students;
    string line;
    while (getline(in, line)) {
        if (line.empty()) continue;
        istringstream ss(line);
        Student s;
        bool ok = bool(ss >> s.name);
        for (double &g : s.scores) if (!(ss >> g)) { ok = false; break; }
        if (ok) students.push_back(s);
    }

    for (const auto& s : students) {
        cout << s.name << ": ";
        double sum = 0;
        for (double g : s.scores) { cout << g << ' '; sum += g; }
        cout << "avg=" << sum / s.scores.size() << '\n';
    }
}

Troubleshooting tips grounded in your thread:

If your file starts with names, extracting into int arrays will fail immediately; parse the name first.
Do not loop on a fixed counter like while(size==debug); loop until input fails.
If names can contain spaces, use a delimiter (e.g., CSV) and split accordingly.
To access a specific row/column of numeric data later, load into vector<vector<double>> and use grid[row][col].

See std::ifstream, operator>>, and std::getline for details.

All 4 Replies

zortec 11 Junior Poster

16 Years Ago

You should check first to see if the file has been opened.

ifstream inFile;

if (!inFile) {
cerr << "Unable to open file input.txt";
    exit(1);   // call system to stop
}

Once you have done that, read from the stream the same way you do cin.

int sum = 0;
int x;

while (inFile >> x)
sum += x;

inFile.close();

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josey_matt 0 Newbie Poster · Answer 1 · 2009-11-29T01:53:07+00:00

i did that but it still doesn't work. the thing i dont get is that after initializing the array elements to 0

for(int i=0;i<size;i++)
	{
		test1[i]=0;
		test2[i]=0;
		test3[i]=0;
		test4[i]=0;
		test5[i]=0;
	}

and after i read this:

while(size==debug)
	{
		for(int i=0;i<size;i++)
		{
			infile>>test1[i];
			infile>>test2[i];
			infile>>test3[i];
			infile>>test4[i];
			infile>>test5[i];
		}
		debug--;
	}

but when i print it. all that comes out is the 0's

for(int i=0;i<size;i++)
	{
		cout<<test1[i]<<" "<<test2[i]<<" "<<test3[i]<<" "<<test4[i]<<" "<<test5[i]<<" "<<endl;
	}

Attached is the output file

programmersbook 17 Junior Poster · Answer 2 · 2009-11-29T04:50:32+00:00

like this?

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

//void calculateAverage();
//int calculateGrade();
//void updateFrequency();

int main()
{
	//const int size=10;
	//int debug=size;
    string tmp;
	//int test1[size], test2[size], test3[size], test4[size], test5[size];
	
	ifstream infile;
	/*
	for(int i=0;i<size;i++)
	{
		test1[i]=0;
		test2[i]=0;
		test3[i]=0;
		test4[i]=0;
		test5[i]=0;
	}
*/
	cout<<"Reading from file ''input.txt''..."<<endl;
	infile.open("input.txt");
	
	if( infile ){
	
	    while( getline(infile, tmp ) ){
	        cout << tmp << endl;
	    }
	}
	
/*
	while(size==debug)
	{
		for(int i=0;i<size;i++)
		{
			infile>>test1[i];
			infile>>test2[i];
			infile>>test3[i];
			infile>>test4[i];
			infile>>test5[i];
		}
		debug--;
	}
	
	for(int i=0;i<size;i++)
	{
		cout<<test1[i]<<" "<<test2[i]<<" "<<test3[i]<<" "<<test4[i]<<" "<<test5[i]<<" "<<endl;
	}
	*/
	
	infile.close();
	#ifdef __LINUX 
	system("pause");
	#endif
	return 0;
}

siddiquedu 0 Newbie Poster · Answer 3 · 2013-05-18T10:20:06+00:00

Dear Sir, How can I input fraction number (like 2.345) in a row. How can i select a poit ( in row 1, column 3). If you please response !!!

Reading data from text file - C++

Dani AI

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