How to return an array from a function

Hello,

what I want my program to do is the following:
1. generate an array of N random numbers in a function
2. return that array to the main function
3. display the contents of this array (later ofcourse I want to do other things with it, but this is the easiest thing for now)

What I have for code is:

Code:

---

/*
Header: iostream
Reason: Input/Output stream
Header: stdlib
Reason: For functions rand and srand
Header: time.h
Reason: For function time, and for data type time_t
*/

#include <iostream>
#include <cstdlib>
#include <time.h>

using namespace std;

int randomRange(int min, int max,int number);


int main()
{
    int list2=randomRange(10,20,10);
    for(int x=0;x<10;x++){
        cout<<list2[x]<<endl;
    }
}

int randomRange(int min, int max, int number)
{
    //Make the seed for the random function
    time_t seed;
    time(&seed);
    srand((unsigned int) seed);


    int list[number];

    //get a random number from range min-max
    int rnumber;
    for(int i=0;i < number;i++){
        rnumber=rand() % (max-min) + min;
        list[i]=rnumber;
        cout<<rnumber<<endl;
        }
    return list;
}

---

Could you please tell me what I'm doing wrong? =)

You can not return an array from anything in C or C++. Since this is C++, perhaps you would like to return a std::vector instead?

Otherwise, the customary method for doing this is by passing in an array (and a size) and filling it in inside the function. Since arrays turn into pointers, you can modify any array passed to a function.

--
Mats

So you mean something like this?

Code:

---

/*
Header: iostream
Reason: Input/Output stream
Header: stdlib
Reason: For functions rand and srand
Header: time.h
Reason: For function time, and for data type time_t
*/

#include <iostream>
#include <cstdlib>
#include <time.h>

using namespace std;

void randomRange(int min, int max,int number, int *pointer);          //Changed


int main()
{
    int array[100];                              //Changed
    void randomRange(10,20,100,array);          //Changed
    for(int x=0;x<100;x++){
        cout<<array[x]<<endl;                    //Changed
    }
}

int randomRange(int min, int max, int number, int *pointer)            //Changed
{
   
    //Make the seed for the random function
    time_t seed;
    time(&seed);
    srand((unsigned int) seed);

    //get a random number from range min-max
    int rnumber;
    for(int i=0;i < number;i++){
        rnumber=rand() % (max-min) + min;
        pointer[i]=rnumber;                                            //Changed
        cout<<rnumber<<endl;
        }
    return;                                                            //Changed
}

---

Something like that, but your program still has a number of errors. Your prototype for randomRange as void, then define it as returning an int. It then returns nothing. You also decorate the call to it in main with "void".

Anyway, look at the compile errors you get when you try to compile.

Ok I got that figured out now,
new problem that I actually don't understand.
I have now two functions: avgi and avgf which as input have a pointer and a size of the array.
They return the avarages of the arrays one for integers and one for floats.
The error I get is: Undefined reference to `avgi(int*,int)' on line 72.
I dont get this since I use both functions the same way, the only difference is that one accepts an array of integers and the other an array of floats.

Code:

Code:

---

/*
Header: iostream
Reason: Input/Output stream
Header: stdlib
Reason: For functions rand and srand
Header: time.h
Reason: For function time, and for data type time_t
*/

#include <iostream>
#include <cstdlib>
#include <time.h>
#include <cmath>


using namespace std;

float avgf(float *arrayf,int sizearrayf);
float avgi(int *arrayi,int sizearrayi);
void avarages(int MinimumRange,int MaximumRange,int NumberOfHits,int TimesShoot,float *AvgPointer);
void randomRange(int min, int max,int number, int *pointer);


int main()
{
    float Tavg=0.0;
    float stdcount=0.0;
    float StandardDeviation=0.0;
    int NumberOfHits,MinimumRange,MaximumRange,TimesShoot;

    //Make the seed for the random function
    time_t seed;
    time(&seed);
    srand((unsigned int) seed);

    cout<<"What is your minimum damage\n";
    cin>>MinimumRange;
    cout<<"What is your maximum damage\n";
    cin>>MaximumRange;
    cout<<"How many hits does your attack make?\n";
    cin>>NumberOfHits;
    cout<<"Damge range:"<<MinimumRange<<"-"<<MaximumRange<<"\nHits:"<<NumberOfHits<<endl;
    cout<<"How often do you want to shoot?"<<endl;
    cin>>TimesShoot;
    float avgarray[TimesShoot];
    avarages(MinimumRange,MaximumRange,NumberOfHits,TimesShoot,avgarray);
    Tavg=avgf(avgarray,TimesShoot);
    for(int x=0;x<TimesShoot;x++)
    {
        stdcount=stdcount+((avgarray[x]-Tavg)*(avgarray[x]-Tavg));
    }
    StandardDeviation=sqrt(stdcount/TimesShoot);
    cout<<"Avarage over time="<<Tavg<<endl;
    cout<<"Standard deviation="<<StandardDeviation<<endl;
}

void avarages(int MinimumRange,int MaximumRange,int NumberOfHits,int TimesShoot,float *AvgPointer)
{

    for(int i=0;i<TimesShoot;i++)
    {
        int counter=0;
        float avg=0;
        float avg2=0;
        int array[NumberOfHits];
        randomRange(MinimumRange,MaximumRange,NumberOfHits,array);
        for(int x=0;x<NumberOfHits;x++)
        {
            counter=counter+array[x];
        }
        avg=(float)counter/NumberOfHits;
      avg2=avgi(array,NumberOfHits);
        cout<<"Avarage for shot nr."<<i+1<<" is: "<<avg<<endl;
        cout<<"new function: "<<avg2<<endl;
        AvgPointer[i]=avg;
    }
    return;
}
void randomRange(int min, int max, int number, int *HitsPointer)
{
    //get a random number from range min-max
    int rnumber;
    for(int i=0;i < number;i++)
    {
        rnumber=rand() % (max-min) + min;
        HitsPointer[i]=rnumber;
    }
    return;
}
float avgf(float *arrayf,int sizearrayf)
{
    float counter=0.0;
    float avg=0.0;
    for(int i=0;i<sizearrayf;i++)
    {
        counter=counter+arrayf[i];
    }
    avg=counter/sizearrayf;
    return avg;
}

float avgi(float *arrayi,int sizearrayi)
{
    float counter=0.0;
    float avg=0.0;
    for(int i=0;i<sizearrayi;i++)
    {
        counter=counter+arrayi[i];
    }
    avg=counter/sizearrayi;
    return avg;
}

---

Code:

---

float avgi(float *arrayi,int sizearrayi)

---

--
Mats

How simple a solution can sometimes be...

Thank you for the help =)

Note also that in C++ you can actually have two functions called exactly the same thing, as long as they take different (types or number of) parameters. So you can have a function called float avg(float *, int n) and a float avg(int *, int n);

--
Mats

Code:

---

int TimesShoot;
cin>>TimesShoot;
float avgarray[TimesShoot];

---

How is this possible? I didn't think an array could be created like that, since TimesShoot is not a const.
I thought you had to do something like:

Code:

---

int *array = NULL;
int n;
cin >> n;
array = new int[n];

---

Quote:

---

Originally Posted by Cpro

Code:

---

int TimesShoot;
cin>>TimesShoot;
float avgarray[TimesShoot];

---

How is this possible? I didn't think an array could be created like that, since TimesShoot is not a const.
I thought you had to do something like:

Code:

---

int *array = NULL;
int n;
cin >> n;
array = new int[n];

---

---

Many compilers allow the first construct as an extension above and beyond C++ standard, but yes, it's not allowed in the C++ standard.

--
Mats

it's defined by C99 right?

Quote:

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Originally Posted by pheres

it's defined by C99 right?

---

Yes, variable length arrays are a C99 feature, but even C++0x is unlikely to have them.