College Lesson Trouble With Count/Sentinel Control Loops

Hi,

This is my first post here and I am in need with some help(might need a lot) with a lesson my professor has given me to help me understand loops.

Here is an imgur link to my current homework. http://i.imgur.com/9Mcja.jpg

As you can see on there I have them listed on which ones are supposed to be sentinel and which ones are supposed to be count control loops.

This is currently what I have:

Code:

---

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

void main()
{
        int count = 0;
        int sum = 0;
        int num;

        ofstream fileout;
        ifstream filein;


        filein.open("C:\\Users\\commiedic\\Desktop\\New folder\\datafile2.txt");
        fileout.open("C:\\Users\\commiedic\\Desktop\\New folder\\answers.txt");

        sum=0;
        filein>>num;
        filein.get(inchar);
        while(filein)
        { sum=sum+num;}


}

---

This class has me stumped currently and I am having a hard time breezing through the class at my instructors speed. So I don't want to get too far behind.

Right now this program is giving me an error that opens CMD and gives me infinite lines of "0's".

can't find the edit button, but I meant to say this is what I have so far. I am stuck on (A) trying to write to the ANSWER.txt file.

You have an input statement after you open your file, but you don't have one in the loop. All it does is keep adding num to sum over and over again. You need to add an input statement to your loop so that it actually reads a new line of the file each time it loops.

Sorry it has been so long for me to reply. rough week...

Here is my updated code

Code:

---

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

void main()
{
        int count = 0;
        int sum = 0;
        int num;

        ofstream fileout;
        ifstream filein;


        filein.open("E:\\*****\\datafile2.txt");
        fileout.open("E:\\*****\\answers.txt");

        sum=0;
        filein>>num;
        while(filein)
        {

                filein>>num;
                fileout<<num;
               
        }


}

---

So this will write to my answers.txt file, but for some reason it skips the first integer "55" and starts at the second integer "67"

What the DataFile2 looks like:

Code:

---

55 67 458 23 81 33
782 375 528
405 324 950 46
14 864 551 38 167 518 630

---

What my answers.txt file looks like:

Code:

---

67458238133782375528405324950461486455138167518630630

---

Of course it does. Just look at your code.

Code:

---

        filein>>num;
        while(filein)
        {

                filein>>num;
                fileout<<num;
               
        }

---

You should reverse the order of your statements in the while loop.

Quote:

---

Originally Posted by GCDEF

You should reverse the order of your statements in the while loop.

---

Awesome thanks! For some reason I am also having trouble keeping the spaces and end line codes.

I got it with:

fileout<<num<<" ";

Quote:

---

Originally Posted by commiedic

Awesome thanks! For some reason I am also having trouble keeping the spaces and end line codes.

I got it with:

fileout<<num<<" ";

---

I'm not sure you got my point. You read from the file twice before you output, so the first input was thrown away. By swapping the lines inside your while statement, you output the first input, and you terminated the loop when the file reached the end, without trying to output the failed input.

Ok I see what you are saying. Here is my new updated code. I will be moving on to the averages now.

Ok, for the averages of the numbers here is what I am getting in my output file.

Code:

---

55 67 458 23 81 33 782 375 528 405 324 950 46 14 864 551 38 167 518 630 630

---

For some reason it isn't giving me A) the average and B) it is repeating the last number twice.

Here is my code including the averages:

Code:

---

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

void main()
{
        int num, fnum, lnum, sum;
        float average, total, counter;
        char inchar;
        ofstream fileout;
        ifstream filein;


        filein.open("E:\\*****\\datafile2.txt");
        fileout.open("E:\\*****\\answers.txt");

        while(filein)
        {       
                filein>>num;
                fileout<<num<<" ";
               

        }

        total=0;
        counter=0;

        while(filein)
        {
                filein>>num;
                total=total+num;
                counter++;
                average = total/counter;
                fileout<<fixed<<setprecision(3)<<endl<<"The Average from the input file is: "<<average<<endl;
        }
               
}

---

Why do you have two loops?
At the end of the first loop, you're at the end of the file, so the second one won't execute.
You don't compute the average in a while loop. To compute an average, you sum the numbers and divide the sum by the count of the numbers.

You didn't do what I told you to regarding the order of statements.

Quote:

---

Originally Posted by GCDEF

Why do you have two loops?
At the end of the first loop, you're at the end of the file, so the second one won't execute.
You don't compute the average in a while loop. To compute an average, you sum the numbers and divide the sum by the count of the numbers.

You didn't do what I told you to regarding the order of statements.

---

Ok, then I will try to build it into one loop. Hopefully I got what you were saying this time. I think I understand that I was being redundant.

So with this new build I am getting the average after every number:

Code:

---

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

void main()
{
        int num, fnum, lnum, sum;
        float average, total, counter;
        char inchar;
        ofstream fileout;
        ifstream filein;


        filein.open("E:\\*****\\datafile2.txt");
        fileout.open("E:\\*****\\answers.txt");


        total=0;
        counter=0;
        while(filein)
        {       
                fileout<<num<<" "<<endl;
                total=total+num;
                counter++;
                average = total/counter;
                fileout<<fixed<<setprecision(3)<<endl<<"The Average from the input file is: "<<average<<endl;
               

        }

               
}

---

Output is:

Code:

---

55

The Average from the input file is: 55.000
67

The Average from the input file is: 61.000
458

The Average from the input file is: 193.333
23

The Average from the input file is: 150.750
81

The Average from the input file is: 136.800
33

The Average from the input file is: 119.500
782

The Average from the input file is: 214.143
375

The Average from the input file is: 234.250
528

The Average from the input file is: 266.889
405

The Average from the input file is: 280.700
324

The Average from the input file is: 284.636
950

The Average from the input file is: 340.083
46

The Average from the input file is: 317.462
14

The Average from the input file is: 295.786
864

The Average from the input file is: 333.667
551

The Average from the input file is: 347.250
38

The Average from the input file is: 329.059
167

The Average from the input file is: 320.056
518

The Average from the input file is: 330.474
630

The Average from the input file is: 345.450
630

The Average from the input file is: 359.000

---

I would like for it to read one line with all the numbers and then one line saying the average of all the numbers is ___

Did you see where I said "You don't compute the average in a while loop. To compute an average, you sum the numbers and divide the sum by the count of the numbers."?

You need to think a little bit about what you're doing. You get an average by getting the sum over the numbers, then dividing by the count of the numbers. That's not what you're doing. You need to get the sum and the count in the loop, but the average after the loop.

Quote:

---

Originally Posted by GCDEF

Did you see where I said "You don't compute the average in a while loop. To compute an average, you sum the numbers and divide the sum by the count of the numbers."?

You need to think a little bit about what you're doing. You get an average by getting the sum over the numbers, then dividing by the count of the numbers. That's not what you're doing. You need to get the sum and the count in the loop, but the average after the loop.

---

Ok I think I see what you are saying now. I will revise my code after my next class. Thank you for being so helpful.

This is the only way I could get it to work. Although it is still repeating the last number twice, but it is giving me the average.

Code:

---

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

void main()
{
        int num, fnum, lnum, sum;
        float average, total, counter;
        char inchar;
        ofstream fileout;
        ifstream filein;


        filein.open("E:\\Resource Files\\datafile2.txt");
        fileout.open("E:\\Resource Files\\answers.txt");


        total=0;
        counter=0;
        while(filein)
        {       
                filein>>num;
                fileout<<num<<" ";
                total=total+num;
                counter++;
        }

        average = total/counter;
        fileout<<fixed<<setprecision(3)<<endl<<"The Average from the input file is: "<<average<<endl;

               
}

---

Code:

---

55
67
458
23
81
33
782
375
528
405
324
950
46
14
864
551
38
167
518
630
630

The Average from the input file is: 359.000

---

Now is there anyway I can get the third step of this assignment in the same program? I am having an issue figuring out how to get the average of the first twelve without having a separate program to do it.

I hadn't read the original assignment about performing the tasks separately, but he shows you what you need to do. You will need multiple loops closing and reopening the file between them.

I've answered your question about repeating the last number several times now. You were on the right track earlier when you read the file before your loop, but you need to put the output before the input in the loop.

Quote:

---

Originally Posted by GCDEF

I hadn't read the original assignment about performing the tasks separately, but he shows you what you need to do. You will need multiple loops closing and reopening the file between them.

I've answered your question about repeating the last number several times now. You were on the right track earlier when you read the file before your loop, but you need to put the output before the input in the loop.

---

Ok I got it =P

Code:

---

total=0;
        counter=0;
        filein>>num;
        while(filein)
        {       
               
                fileout<<num<<" ";
                filein>>num;
                total=total+num;
                counter++;
        }

        average = total/counter;
        fileout<<fixed<<setprecision(3)<<endl<<"The Average from the input file is: "<<average<<endl;

---

Chapter 8 assignment is where we do multiple loops using void functions... So I guess I need to do a separate print out for each one.

Looks like all the steps, a, b, c, d... he asks you to "reread" the file, which would require separate loops and closing and opening the file between each loop.

concerning reading last value twice ... you have

Code:

---

while (filein)
{       
  filein>>num;
  fileout<<num<<" ";
  total=total+num;
  counter++;
}

---

You are reading the last value, and adding to total (so far so good).

Then it goes back to the start of the loop : while (filein)
This still will result in "true", so you enter the body of the loop again.

generally, you should loop as follows:

Code:

---

while (filein >> num)
{
  total += num;
  ++counter;
}

---

Whoa... look at me go lol Thanks!

Code:

---

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

void main()
{
        int num, fnum, lnum, sum;
        float average, total, counter;
        char inchar;
        ofstream fileout;
        ifstream filein;

        fileout.open("E:\\Resource Files\\answers.txt");
        filein.open("E:\\Resource Files\\datafile2.txt");
       


        total=0;
        counter=0;
        filein>>num;
        while(filein)
        {       
               
                fileout<<num<<" ";
                filein>>num;
                total=total+num;
                counter++;
        }

        average = total/counter;
        fileout<<fixed<<setprecision(3)<<endl<<"The Average from the input file is: "<<average<<endl;

        filein.close();
        filein.clear();
       
        filein.open("E:\\Resource Files\\datafile2.txt");

        total=0;
        counter=1;
        while(counter <=12)
        {
                        filein>>num;
                        total=total+num;
                        counter++;
        }

        average=total/12;
        fileout<<"The average of the first 12 integers of the input file is: "<<average<<endl;


               
}

---

Code:

---

55 67 458 23 81 33 782 375 528 405 324 950 46 14 864 551 38 167 518 630
The Average from the input file is: 374.200
The average of the first 12 integers of the input file is: 340.083

---

Ok, Now I had friend give me a hint on this next piece for reading every 3rd integer in the input file, but I don't know how to decipher it.

if(num%3==0)

I get that I will need an "if" statement, but what does "num%3==0" mean?!

Remember elementary school division? 5 divided by 3 = 1 remainder 2, for example. The modulo operator gives you the remainder, so 5 % 3 would return 2. If it equals zero, the numerator is evenly divisible by the denominator.

Quote:

---

Originally Posted by GCDEF

Remember elementary school division? 5 divided by 3 = 1 remainder 2, for example. The modulo operator gives you the remainder, so 5 % 3 would return 2. If it equals zero, the numerator is evenly divisible by the denominator.

---

Ok, so the if statements expression is only true if the remainder of the num%3 equals 0. So if there is no remainder than it is a true statement.

Pretty sure I got the code right, but I am coming up with a different answer than what I was expecting

Code:

---

55 67 458 23 81 33 782 375 528 405 324 950 46 14 864 551 38 167 518 630
The Average from the input file is: 374.200
The average of the first 12 integers of the input file is: 340.083
The sum of every third number is: 3870.000

---

Code:

---

        filein.close();
        filein.clear();
       
        filein.open("E:\\Resource Files\\datafile2.txt");

        total=0;
        while(filein)
        {
                filein>>num;
                if(num%3==0)
                total=total+num;
        }

        fileout<<"The sum of every third number is: "<<total<<endl;
               
}

---

From adding every 3rd number I am getting 3000 as my answer.

Quote:

---

Originally Posted by commiedic

Ok, so the if statements expression is only true if the remainder of the num%3 equals 0. So if there is no remainder than it is a true statement.

---

Yes. Typically C and C++ programmers start counters at 0, so if your loop included if(counter % 3) == 0) then every third time through the loop, beginning with the first time, would be true.

Quote:

---

Originally Posted by commiedic

Pretty sure I got the code right, but I am coming up with a different answer than what I was expecting

Code:

---

55 67 458 23 81 33 782 375 528 405 324 950 46 14 864 551 38 167 518 630
The Average from the input file is: 374.200
The average of the first 12 integers of the input file is: 340.083
The sum of every third number is: 3870.000

---

Code:

---

        filein.close();
        filein.clear();
       
        filein.open("E:\\Resource Files\\datafile2.txt");

        total=0;
        while(filein)
        {
                filein>>num;
                if(num%3==0)
                total=total+num;
        }

        fileout<<"The sum of every third number is: "<<total<<endl;
               
}

---

From adding every 3rd number I am getting 3000 as my answer.

---

You really need to think about what you're doing. num could be anything. num isn't the value you want to be testing here.

Quote:

---

Originally Posted by commiedic

Ok I got it =P

Code:

---

total=0;
        counter=0;
        filein>>num;
        while(filein)
        {       
               
                fileout<<num<<" ";
                filein>>num;
                total=total+num;
                counter++;
        }

        average = total/counter;
        fileout<<fixed<<setprecision(3)<<endl<<"The Average from the input file is: "<<average<<endl;

---

Chapter 8 assignment is where we do multiple loops using void functions... So I guess I need to do a separate print out for each one.

---

Would an eof() function have worked here as well?

Before worrying about every third number, you should get
the very first part correct: getting the average of all the numbers
in the file.

You have 2 ways of doing that:

1) Take away the read outside of the while loop, and use the while
loop that I posted. (best method)

2) keep you loop as is ... but inside the loop check the state
of the stream. If the stream's state is false, do not add num to total.

l