DaniWeb Forum Index > Software Development > C++

C++ RSS

input, search, output

Please support our C++ advertiser: Intel Parallel Studio Home

•

Join Date: Apr 2009

Posts: 2

Reputation: joozi is an unknown quantity at this point

Solved Threads: 0

joozi

Offline

Newbie Poster

input, search, output

Apr 4th, 2009

Im doing a c++ course at uni and one of my questions is to read in an external file, input a number (like 64) then the program will search the file for the number and output how many times the number the user input comes up in the file.

here is my code;

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
#include <stdlib.h>
#include <iostream.h>
#include <fstream.h>
using namespace std;
 
int main()
{
    int input, count=0, hold;
    ifstream inFile("Problem2.txt");
 
    cout << "Enter a number ";
    cin >> input;
 
    if (!inFile) {
        cout << "Unable to open file";
        return(-1);
    }
 
    int number;
    inFile >> number;
    while(!inFile.eof())
    {
     inFile >> number;
     if(number == input){
      count++;}
    }
    cout << count;
    cin >> hold;
    inFile.close();
}
#include <stdlib.h>
#include <iostream.h>
#include <fstream.h>
using namespace std;

int main()
{
    int input, count=0, hold;
    ifstream inFile("Problem2.txt");
    
    cout << "Enter a number ";
    cin >> input;
    
    if (!inFile) {
        cout << "Unable to open file";
        return(-1);
    }
    
    int number;
    inFile >> number;
    while(!inFile.eof())
    {
     inFile >> number;
     if(number == input){
      count++;}
    }
    cout << count;
    cin >> hold;
    inFile.close();
}

the input file im using is:

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
64
64
92
64
64
55
56
77
75
66
25
35
39
90
19
23
44
45
88
85
15
27
32
44
68
8
0
64
64
92
64
64
55
56
77
75
66
25
35
39
90
19
23
44
45
88
85
15
27
32
44
68
8
0

If i input 64 as my input number it shoud tell me that 64 is in the file 4 times but it only outputs 3, and if i input 0 it should come up once but it comes up twice .I havn't got much experience in c++ so I don't really know what im doing 100%.

•

Join Date: Aug 2005

Posts: 15,442

Reputation: Ancient Dragon has a reputation beyond repute

Solved Threads: 1474

Ancient Dragon Ancient Dragon is offline

Offline

Still Learning

Re: input, search, output

Apr 4th, 2009

The while loop is wrong -- don't need eof()

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
int number;
while( inFile >> number )
{
    // blabla
}
int number;
while( inFile >> number )
{
    // blabla
}

Don't PM me with questions -- you might get a nasty PM in response. If you have a question then post it in one of the forums.

•

Join Date: Apr 2006

Posts: 5,051

Reputation: John A is a splendid one to behold

Solved Threads: 332

John A

Offline

Vampirical Lurker

Re: input, search, output

Apr 4th, 2009

•

Help with Code Tags

C++ Syntax (Toggle Plain Text)
int number;
    inFile >> number;
    while(!inFile.eof())
    {
     inFile >> number;
int number; inFile >> number; while(!inFile.eof()) { inFile >> number;

You're overwriting the first number in the file. You haven't counted whether the first line in the file is the number that the user entered. That's why your program only reported 3 occurrences of 64.

Your second problem is how you're reading your file. The issue with using .eof() to find out if you're at the end of the file is that it only reports an EOF after you've already had an unsuccessful read. So the last line in the file will end up being read twice: the first time correctly, the second time it will read it again and give you an EOF.

So, I recommend using the following method instead:

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
while (inFile >> number)
{
  if (number == input)
  {
    /* etc */
  }
}
while (inFile >> number)
{
  if (number == input)
  {
    /* etc */
  }
}

Then remove the line before the while loop: inFile >> number; , which will solve your first problem.

"Technological progress is like an axe in the hands of a pathological criminal."

All my posts may be freely redistributed under the terms of the MIT license.

•

Join Date: Feb 2009

Posts: 1,968

Reputation: tux4life has a reputation beyond repute

Solved Threads: 214

tux4life

Offline

Posting Virtuoso

Re: input, search, output

Apr 4th, 2009

In one of the last lines I come across the following instruction:
cin >> hold; If you're putting that instruction there to prevent the program from automatically closing: it's better to use cin.get(); instead ...
Please remember to also delete the variable declaration of 'hold' (somewhere in the first lines of your code) ...

"Never argue with idiots, they just drag you down to their level and then beat you with experience."

•

Join Date: Apr 2009

Posts: 2

Reputation: joozi is an unknown quantity at this point

Solved Threads: 0

joozi

Offline

Newbie Poster

Re: input, search, output

Apr 4th, 2009

Thank you, I asked my instructor how to fix it and he told me the .eof was correct. Thanks again, can't believe it was that simple.

•

Join Date: Aug 2005

Posts: 15,442

Reputation: Ancient Dragon has a reputation beyond repute

Solved Threads: 1474

Ancient Dragon Ancient Dragon is offline

Offline

Still Learning

Re: input, search, output

Apr 4th, 2009

your instructor is an idiot. Go immediately to another university.

Don't PM me with questions -- you might get a nasty PM in response. If you have a question then post it in one of the forums.

•

Join Date: Apr 2006

Posts: 5,051

Reputation: John A is a splendid one to behold

Solved Threads: 332

John A

Offline

Vampirical Lurker

Re: input, search, output

Apr 4th, 2009

>I asked my instructor how to fix it and he told me the .eof was correct.
Well, there's nothing 'wrong' with eof(), you just need to understand that it will only indicate an EOF after an unsuccessful read. So, for example, you could modify your code to look like:

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
inFile >> number;
while ( !inFile.eof() )
{
  if (number == input)
    count++;
 
  inFile >> number;
}
inFile >> number;
while ( !inFile.eof() )
{
  if (number == input)
    count++;

  inFile >> number;
}

This works because it checks for an EOF after you've tried reading from the file. If there's no EOF, it goes ahead and processes the input, and then attempts another read.

Of course, if your instructor told you that your use of eof() was correct, then they really are an idiot.

Last edited by John A; Apr 4th, 2009 at 10:10 pm.

"Technological progress is like an axe in the hands of a pathological criminal."

All my posts may be freely redistributed under the terms of the MIT license.

•

Join Date: May 2006

Posts: 3,114

Reputation: WaltP has much to be proud of

Solved Threads: 281

WaltP

Offline

Posting Sensei

Re: input, search, output

Apr 5th, 2009

And to prove that he's an..., try this:

 Help with Code Tags 
 cpp Syntax (Toggle Plain Text) 
#include <iostream>
#include <fstream>
using namespace std;
 
int main()
{
    char line[80];
    ifstream inFile("x.x");
 
    while (!inFile.eof())
    {
        inFile >> line;
        cout << line << ' ';
    }
    inFile.close();
    return 0;
}
#include <iostream>
#include <fstream>
using namespace std;

int main()
{
    char line[80];
    ifstream inFile("x.x");
    
    while (!inFile.eof())
    {
        inFile >> line;
        cout << line << ' ';
    }
    inFile.close();
    return 0;
}