Beginner question to shuffling arrays , and input and output to a function

Hey Everyone.


I am relatively new to C++, I have only started learning it this year.
I am having trouble writing a little program to take in a text document and store it in an array. Then take that array and randomise the values in a certain way. It is for a rostering program to arrange the riders + horses into suitable positions.


What I am trying to attempt in this function (gen() ) is to copy the entry[num] to entry2[num2] . Where num is the amount of entries there are, and num2 is a randomly generated rand() number. I then wanted it to check if the new entry is atleast 15 positions more then the old entry (in this case.. so the rider of the horse can have a break before his next event)


so as you can guess .. this application doesnt work, im guessing there is an easier way?
How can I send the variables into this array, And how can I get this function to return the array back to my main .. im guessing via a pointer?


I have attached the whole code below.


Thankyou.
Sam.

Code:

/*   ________________________________________________________________________________
*    |   TITLE:     main.cpp                                                        |
*    |   AUTHOR:    Samuel Abbott (samuel.d.abbott@gmx.com)                         |
*    |   PURPOSE:   to take camp draft data in, randomise it with certain values,   |
*    |              and output the new roster as a text document                    |
*    |   DATE:      may 1, 2012                                                     |
*    |   LAST EDIT: may 3,2012                                                      |
*    |______________________________________________________________________________|
*/

#include <iostream>
#include <string>
#include <stdlib.h> //random number
#include <time.h> //random number
#include <fstream> //used for input / output of external files

using namespace std;
/*
*   TITLE: gen
*   PURPOSE: to randomise the entries , check to see if they are more then 15 units apart, and return a pointer to the randomised array
*   string entry[] holds original values
*   int num [] holds number of entries
*/
sting gen(string entry[], int num)
{
    int count = 0;
    string entry2[num]; //randomised array

    /* initialize random seed: */
        srand ( time(NULL) );
    for(count =0; count < num)
    {
        num2 = rand() % num; //generate random number
        entry[num] = entry2[num2]; //copy number from array to a random position in the next array

        /* a series of if checks to make sure the entry is no less then 15 positions from the previous entry */
        if(entry2[num2]=entry[num-15])
        {
            num2 = rand() % num; //generate random number
            entry[num] = entry2[num2]; //copy number from array to a random position in the next array
        }
        else if(entry2[num2]=entry[num-14])
        {
            num2 = rand() % num; //generate random number
            entry[num] = entry2[num2]; //copy number from array to a random position in the next array
        }
        else if(entry2[num2]=entry[num-13])
        {
            num2 = rand() % num; //generate random number
            entry[num] = entry2[num2]; //copy number from array to a random position in the next array
        }
        else if(entry2[num2]=entry[num-12])
        {
            num2 = rand() % num; //generate random number
            entry[num] = entry2[num2]; //copy number from array to a random position in the next array
        }
        else if(entry2[num2]=entry[num-11])
        {
            num2 = rand() % num; //generate random number
            entry[num] = entry2[num2]; //copy number from array to a random position in the next array
        }
        else if(entry2[num2]=entry[num-10])
        {
            num2 = rand() % num; //generate random number
            entry[num] = entry2[num2]; //copy number from array to a random position in the next array
        }
        else if(entry2[num2]=entry[num-9])
        {
            num2 = rand() % num; //generate random number
            entry[num] = entry2[num2]; //copy number from array to a random position in the next array
        }
        else if(entry2[num2]=entry[num-8])
        {
            num2 = rand() % num; //generate random number
            entry[num] = entry2[num2]; //copy number from array to a random position in the next array
        }
        else if(entry2[num2]=entry[num-7])
        {
            num2 = rand() % num; //generate random number
            entry[num] = entry2[num2]; //copy number from array to a random position in the next array
        }
        else if(entry2[num2]=entry[num-6])
        {
            num2 = rand() % num; //generate random number
            entry[num] = entry2[num2]; //copy number from array to a random position in the next array
        }
        else if(entry2[num2]=entry[num-5])
        {
            num2 = rand() % num; //generate random number
            entry[num] = entry2[num2]; //copy number from array to a random position in the next array
        }
        else if(entry2[num2]=entry[num-4])
        {
            num2 = rand() % num; //generate random number
            entry[num] = entry2[num2]; //copy number from array to a random position in the next array
        }
        else if(entry2[num2]=entry[num-3])
        {
            num2 = rand() % num; //generate random number
            entry[num] = entry2[num2]; //copy number from array to a random position in the next array
        }
        else if(entry2[num2]=entry[num-2])
        {
            num2 = rand() % num; //generate random number
            entry[num] = entry2[num2]; //copy number from array to a random position in the next array
        }
        else if(entry2[num2]=entry[num-1])
        {
            num2 = rand() % num; //generate random number
            entry[num] = entry2[num2]; //copy number from array to a random position in the next array
        }
        else
        {
            entry[num] = entry2[num2];
        }
    }
    string pointer* = entry2[]
    return pointer
}

/*
*   Title : Loading
*   Purpose: This function generates a loading animation. in other words. just a fancy graphic.
*   HAS NO LOADING PURPOSE
*/

void loading()
{
    /* Declare loading variable, this variable is just the screen printout */
    string loading = "...";
    int time = 0;
    int loadtime = 10;

    /* print out loading animation */
    while(time != loadtime)
        {
            cout << loading;
            time++;
        }

}
void loading();

/*
*   Title: Main
*   Purpose: this is the main function for the randomisation program
*/
int main()
{
    //declare all variables
    string fname = "";
    int count;

    string line;
    ifstream inputfile;
    char c;
    int num=0;


    /* introduction */
    cout << "Roster Randomisation Generator" << endl;
    /* Get input for roster name */
    cout << "Enter a name for the roster, such as 13022012coolah:"<<endl;
    cin>> fname;
    /* Begin generating roster */
    cout << "Roster Generation in progress." << endl;
    loading();
    /* get amount of lines in text file .. used to determine how many entries there are to avoid printing blank spaces*/

        inputfile.open ("output.txt");
            while (inputfile.good())
            {
                c = inputfile.get();
                if (c=='\n')num++;
            }
        inputfile.close();
    cout<<"Number of Entries counted is: "<<num<<endl;

string entry[num];

    cout << "Grabbing entries from entry file..."<<endl;
    /* open text file*/
    inputfile.open ("output.txt");
    /* read all data into the array entry[] */
    for (count = 0; count < num; count++)
        {
            getline (inputfile,line); //Gets a single line from example.txt
            entry[count]=line;

           // inputfile >> entry[count];
        }
    inputfile.close();
    cout <<"Found the following entries: " <<endl;
    /* output captured entries*/
    for(count =0; count < num; count++)
        cout <<entry[count] <<endl;


    return 0;
}

> for(count =0; count < num)
Does this even compile?

> if(entry2[num2]=entry[num-15])
All these assignments (=) need to be comparisons (==)

I suggest you write out fifteen times:
"I will use loops instead of copying and pasting code".

Well I'm just kidding really, but I'd like to do you a favour by urging you to have a go at converting that repetitive code into a loop. Don't worry, we'll help you if you can't quite get it right.
If you grader is anything like me then he will also be facepalming at this, and you don't want that.

Oh another really big hint: Turn your warning levels up and make sure you pay attention to them.

Originally Posted by Salem

> for(count =0; count < num)
Does this even compile?

as i found out .. no

> if(entry2[num2]=entry[num-15])
All these assignments (=) need to be comparisons (==)

EDIT:
@imalc - I will have a go at it now ... only just noticed your reply.
i am using code::blocks on linux .. and it only seems to spit out my warning when i hit the compile button.
i am facepalming myself over this haha.


so i have made a few more amendments to the code . and i do believe its the for() loop that is causing me grief now .. What would be the best loop to use for this function ?

i posted my amended code, and the error log. the code starts from line 24

Code:

string gen(string[], int num)
{
    int count = 0;
    int num2 = 0;
    string entry2[num]; //randomised array

    /* initialize random seed: */
        srand ( time(NULL) );
    for(count =0; count < num)
    {
        num2 = rand() % num; //generate random number
        entry[num] = entry2[num2]; //copy number from array to a random position in the next array

        /* a series of if checks to make sure the entry is no less then 15 positions from the previous entry */
        if(entry2[num2]==entry[num-15])
        {
            num2 = rand() % num; //generate random number
            entry[num] = entry2[num2]; //copy number from array to a random position in the next array
        }
        else if(entry2[num2]==entry[num-14])
        {
            num2 = rand() % num; //generate random number
            entry[num] = entry2[num2]; //copy number from array to a random position in the next array
        }
        else if(entry2[num2]==entry[num-13])
        {
            num2 = rand() % num; //generate random number
            entry[num] = entry2[num2]; //copy number from array to a random position in the next array
        }
        else if(entry2[num2]==entry[num-12])
        {
            num2 = rand() % num; //generate random number
            entry[num] = entry2[num2]; //copy number from array to a random position in the next array
        }
        else if(entry2[num2]==entry[num-11])
        {
            num2 = rand() % num; //generate random number
            entry[num] = entry2[num2]; //copy number from array to a random position in the next array
        }
        else if(entry2[num2]==entry[num-10])
        {
            num2 = rand() % num; //generate random number
            entry[num] = entry2[num2]; //copy number from array to a random position in the next array
        }
        else if(entry2[num2]==entry[num-9])
        {
            num2 = rand() % num; //generate random number
            entry[num] = entry2[num2]; //copy number from array to a random position in the next array
        }
        else if(entry2[num2]==entry[num-8])
        {
            num2 = rand() % num; //generate random number
            entry[num] = entry2[num2]; //copy number from array to a random position in the next array
        }
        else if(entry2[num2]==entry[num-7])
        {
            num2 = rand() % num; //generate random number
            entry[num] = entry2[num2]; //copy number from array to a random position in the next array
        }
        else if(entry2[num2]==entry[num-6])
        {
            num2 = rand() % num; //generate random number
            entry[num] = entry2[num2]; //copy number from array to a random position in the next array
        }
        else if(entry2[num2]==entry[num-5])
        {
            num2 = rand() % num; //generate random number
            entry[num] = entry2[num2]; //copy number from array to a random position in the next array
        }
        else if(entry2[num2]==entry[num-4])
        {
            num2 = rand() % num; //generate random number
            entry[num] = entry2[num2]; //copy number from array to a random position in the next array
        }
        else if(entry2[num2]==entry[num-3])
        {
            num2 = rand() % num; //generate random number
            entry[num] = entry2[num2]; //copy number from array to a random position in the next array
        }
        else if(entry2[num2]==entry[num-2])
        {
            num2 = rand() % num; //generate random number
            entry[num] = entry2[num2]; //copy number from array to a random position in the next array
        }
        else if(entry2[num2]==entry[num-1])
        {
            num2 = rand() % num; //generate random number
            entry[num] = entry2[num2]; //copy number from array to a random position in the next array
        }
        else
        {
            entry[num] = entry2[num2];
        }
    }
    string &pointer = entry2[];
    return pointer;
}

error log:

/home/samuel/Projects/campd/campdraft/main.cpp||In function ‘std::string gen(std::string*, int)’:|
/home/samuel/Projects/campd/campdraft/main.cpp|32|error: expected ‘;’ before ‘)’ token|
/home/samuel/Projects/campd/campdraft/main.cpp|35|error: ‘entry’ was not declared in this scope|
/home/samuel/Projects/campd/campdraft/main.cpp|118|error: expected primary-expression before ‘]’ token|
||=== Build finished: 3 errors, 0 warnings ===|

I guess it's because your for loop construct is still broken.

Go read your book again, and note how many expressions and ; a proper for loop has.

Code:

and it only seems to spit out my warning when i hit the compile button.

thats right, because you are not using an interpreter.

There are actually two problems here. The first one is to find an algorithm that re-orders the array the way you want, and the second one is to translate it into a correct c++ program.

To re-arrange the array so that all elements move at least 'n' positions AND to do it in a random way is tricky.

Your attempt to solve this is - as far as I understand it:

Code:

for each array index
  repeat
    new_index = random
  until distance(old_index, new_index) >= 15
  copy element
end

But does it work? Let's say your array size is 7 and the minimum distance is 2.

Code:

[a][b][c][d][e][f][g] original array

re-arrange the elements:

[ ][ ][ ][ ][ ][ ][a] a: random index 6 -> OK
[ ][ ][ ][b][ ][ ][a] b: random index 3 -> OK
[c][ ][ ][b][ ][ ][a] c: random index 0 -> OK
[c][d][ ][b][ ][ ][a] d: random index 1 -> OK
[c][d][e][b][ ][ ][a] e: random index 2 -> OK
[c][d][e][b][ ][ ][a] f: no valid position left...

See? It may or may not work, depending on the random index sequence.

You should try to find an algorithm (that is guaranteed to work) first, and then figure out how to implement it in c++.