Problems with putting the output in the main function in c++

Question

i want to put the input for n / anzahl and the output of the minimum and maximum temperature in the main function while having the calculation in the void function. i think my mistake is by calling the wrong reference but i can't see it. can someone help me see my mistake?

i got this so far. this code is everything in the main function, it works perfectly but i have problems with the realization of putting the output in the main function

#include <iostream>
#include <iostream>
#include <cstdlib>
#include <vector>
#include <cmath>
#include <iomanip>

using namespace std;

int main()
{


    int n,i;
    int groesst, kleinst;
    int rand(void);
    cout << "Geben Sie Anzahl der Temperaturwerte an: "; //put in the amount of temperatures
    cin >> n;
    n=n+1; //so non programmers arent confused


    vector<int> temp(n);
    cout << "31 zufaellige Temperaturen:\n" << endl;
    groesst = temp[0];
    kleinst = temp[0];
     for (i=1;i<n;i++)
    {
        temp[i]=rand()%20-4;//random temperature between -4 and 15
        cout << temp[i] << " Grad Celsius"<< endl;

        if (temp[i]>groesst) //
        {
            groesst = temp[i]; //
        }

        if (temp[i]<kleinst)
        {
            kleinst = temp [i];
        }
    }


    cout << kleinst; //minimum temperature
    cout << "\n";
    cout << groesst; //maximum temperature

 return 0;
}

this is my attempt:

#include <iostream>
#include <iostream>
#include <cstdlib>
#include <vector>
#include <cmath>
#include <iomanip>
using namespace std;

void minmaxim(vector<int>& temp, int& n, int& kleinst, int& groesst)
{
    int i;
    int rand(void);

    temp[n];
    groesst = temp[0];
    kleinst = temp[0];
     for (i=1;i<n;i++)
    {
        temp[i]=rand()%20-4;


        if (temp[i]>groesst)
            groesst = temp[i];
        }

        if (temp[i]<kleinst)
        {
            kleinst = temp [i];
        }
        return;
    }


int main ()
{
    vector<int> temps;
    int anzahl, minimum,maximum;
    cout << "Geben Sie die Anzahl der Temperaturwerte ein: "; //type in the amounts of temperatures
    cin >> anzahl;

   minmaxim(temps, anzahl, minimum, maximum); //calling the function
   cout << " " << anzahl;

    cout << " " << minimum <<endl;
    cout << " " << maximum <<endl;

    return 0;
}

Answer 1

The biggest problem are minimum and maximum are both uninitialized when minmaxim() is called invoking undefined behavior. Before you compare your values, you must initialize maximum and minimum to numbers below, and above, the range of possible temperatures, e.g.

    int anzahl, 
        minimum =  200,     /* initialize min above and max below possible range */
        maximum = -200;

Or, properly covering the entire range of int, e.g.

#define NMAX std::numeric_limits<int>::max()
#define NMIN std::numeric_limits<int>::min()
...
    int anzahl,
        minimum = NMAX,     /* initialize min above and max below possible range */
        maximum = NMIN;

Your use of random values using C rand() has been replaced in C++ with Pseudo-random number generation. You would create and use a random device as follows:

void minmaxim (std::vector<int>& temp, int& n, int& kleinst, int& groesst)
{
    std::random_device rd;    /* delcare the randon number generator device */
    std::mt19937 gen(rd());   /* standard mrsene_twister engine seeded w/rd */
    std::uniform_int_distribution<int> dist(0, NMAX); /* create disribution */

Then calling

int value = dist(rd);

retrieves a random value in the range. You can set the max of range or continue to use the entire range of values and modulo, more or less your choice.

Your use of std::vector is not quite right. std::vector provides the .push_back() member function to add to the vector. your minmaxim () function could be written as:

void minmaxim (std::vector<int>& temp, int& n, int& kleinst, int& groesst)
{
    std::random_device rd;    /* delcare the randon number generator device */
    std::mt19937 gen(rd());   /* standard mrsene_twister engine seeded w/rd */
    std::uniform_int_distribution<int> dist(0, NMAX); /* create disribution */
    
    for (int i = 0; i < n; i++) {
        int randval = dist(rd) % 20 - 4;
        temp.push_back(randval);
        
        if (randval < kleinst)
            kleinst = randval;
        if (randval > groesst)
            groesst = randval;
    }
}

See Why is “using namespace std;” considered bad practice?. Making those changes, you could write your entire source as:

#include <iostream>
#include <vector>
#include <random>

#define NMAX std::numeric_limits<int>::max()
#define NMIN std::numeric_limits<int>::min()

void minmaxim (std::vector<int>& temp, int& n, int& kleinst, int& groesst)
{
    std::random_device rd;    /* delcare the randon number generator device */
    std::mt19937 gen(rd());   /* standard mrsene_twister engine seeded w/rd */
    std::uniform_int_distribution<int> dist(0, NMAX); /* create disribution */
    
    for (int i = 0; i < n; i++) {
        int randval = dist(rd) % 20 - 4;
        temp.push_back(randval);
        
        if (randval < kleinst)
            kleinst = randval;
        if (randval > groesst)
            groesst = randval;
    }
}


int main (void)
{
    std::vector<int> temps{};
    int anzahl,
        minimum = NMAX,     /* initialize min above and max below possible range */
        maximum = NMIN;
    
    std::cout << "Geben Sie die Anzahl der Temperaturwerte ein: ";
    if (!(std::cin >> anzahl)) {
        std::cerr << "error: invalid integer input.\n";
        return 1;
    }

    minmaxim (temps, anzahl, minimum, maximum); 
    
    for (const auto& t : temps)
        std::cout << t << '\n';
    std::cout << "\n " << anzahl << "\n " << minimum << "\n " << maximum << '\n';

    return 0;
}

(note: avoid including unused headers)

Example Use/Output

$ ./bin/maxmintemps
Geben Sie die Anzahl der Temperaturwerte ein: 5
4
-4
8
3
13

 5
 -4
 13

If you wanted to tidy up the output from main() a bit more, you could output the temperature values in lines of 10 with the results below. You could then legitimately include the <iomanip> header to align the temperature values wtih std::setw(). You could replace the current output loop with:

#include <iomanip>
...
    for (size_t i = 0; i < temps.size(); i++) {
        if (i % 10 == 0)
            std::cout.put ('\n');
        std::cout << " " << std::setw(2) << temps[i];
    }
    std::cout << "\n\n anzahl  : " << anzahl << 
                "\n minimum : " << minimum << 
                "\n maximum : " << maximum << '\n';

Updated Output

$ ./bin/randtempchk
Geben Sie die Anzahl der Temperaturwerte ein: 40

  3 13  9  8 12 15  1  0  7  4
 -2 -3  8 14 -4  7 -2  7 -2  2
 10  1 14  7  6  6 13  6  6  0
  5  9  6  8 13  9 14  9 15  6

 anzahl  : 40
 minimum : -4
 maximum : 15

Look things over and let me know if you have further questions.