Dynamic Arrays (beginner level)

[thiskid]

Hey everyone, so today I had a quiz and this program was the quiz question and I could not get it to compile. The lines are 26, 29, and 32 where the errors occurred. Anyone know what the error is? The output is also included but remember that lines are 26, 29, and 32, not the ones stated.


This program has the user enter in an integer and that represents the number of elements of an array. And this code outputs how many numbers are positive and how many numbers are zero.

count.cpp: In function ‘int main()’:
count.cpp:34: error: expected primary-expression before ‘]’ token
count.cpp:37: error: expected primary-expression before ‘]’ token
count.cpp:40: error: expected primary-expression before ‘]’ token

#include <cstdlib>
#include <iostream>

using namespace std;

// FUNCTION PROTOTYPES
void get_list(int list[], int size);
int count_pos(const int list[], int size);
int count_zeros(const int list[], int size);
int main()
{
    int length;
    int num_pos, num_zeros;
    int * list;
    int *size=new int[length];
    
    
    // Prompt and read number of elements from the user into the variable length
    cout << "Enter number of elements: ";
    cin >> length;
    
    // Create a new array (dynamically allocate) of size length and assign it to variable list
    list= new int[length];
    
    // Prompt and read the elements from the user. Call the function get_list
    get_list(list[],size);
    
    // Count the number of positive numbers in the list. Call the function count_pos. Use variable num_pos
    count_pos(list[], size);
    
    // Count the number of zeros in the list. Call the function count_zeros. Use variable num_zeros
    count_zeros(list[],size);
    
    // Display number of positive elements
    cout << " Number of positive elements: " <<  num_pos << endl;
    
    // Display number of zeros
    cout << "Number of zero elements: " << num_zeros << endl;
    
    // De-allocate the list
    delete [] list;
    
    return 0;
}

// FUNCTION DEFINTIONS GO HERE
void get_list(int list[], int size)
{
    int i(0);
    int x(0);
    
    cout << "Enter list: " << endl;
    
    while(i<size)
    {
        cin >> x;
        list[i]=x;
        i++;
    }
    
}

int count_pos(const int list[], int size)
{
    int num_pos(0);
    for(int i=0; i < size; i++)
    {
        if(list[i]>0)
        {
            num_pos++;
        }
    }
}


int count_zeros(const int list[], int size)
{
    int num_zeros(0);
    for(int i=0; i < size; i++)
    {
        if(list[i] == 0)
        {
            num_zeros++;
        }
    }
}

[IWishIKnew]

hmm, study up on how to pass arrays to another function....

[N36fSL3A]

What's the point of declaring the headers twice and use namespace std twice?

[thiskid]

@IWishIKnew. I have done that already. I wish I knew what was different that regular passing. The point of this quiz was to use the [new] and [delete] functions but I don't see how I am passing them incorrectly.

@Lumpkin, My apologies, some reason I pasted the code twice. I have edited it

[TwilightSpectre]

In line 15, you are initializing *size to length, when length has not yet been declared. Also, for your functions, did you want to return anything? I think you may have missed that step for count_pos and count_zeros...

Actually, having now read your code in more detail, why are you dynamically allocating "size" anyway? For the start of your code, just get rid of size, and replace your references to "size" with length for the rest of your code.

[thiskid]

@NT3, so you're saying that I should move line 15 to 21? If so, I still get the same errors. I wonder if I messed up the function prototypes because I don't see how i'm passing the arrays any differently.

Secondly, I did not want to return anything. The quiz stated not to return any values, which I thought was weird, too. This quiz was about dynamically allocating arrays and this was the quiz question. I could have done this without allocating but professor wanted us to allocate.

[IWishIKnew]

well, you could pass the variables by reference and modify them directly.

void modify_a_pointer(int&*);

void modify_some_other_var(int&);

[thiskid]

The quiz had lines 1-14 so we had to use them. And all comments are the steps that the professor wanted us to do. I filled in lines 15 (excluding the comments) So I am not able to pass the variables by reference

[thiskid]

#include <cstdlib>
#include <iostream>

using namespace std;

// FUNCTION PROTOTYPES
void get_list(int list[], int size); //Function prototype that asks the user for the size and number of elements in an array
int count_pos(const int list[], int size); //Function prototype that counts how many positive numbers there are
int count_zeros(const int list[], int size); //Function prototype that counts how many zeros are in the array

int main()
{
  int length;
  int num_pos, num_zeros;
  int * list;
  

  // Prompt and read number of elements from the user into the variable length
  cout << "Enter number of elements: ";
  cin >> length;
  
  // Create a new array (dynamically allocate) of size length and assign it to variable list
 int *size=new int[length];
  list= new int[length];

  // Prompt and read the elements from the user. Call the function get_list
  get_list(list,length);
  
  // Count the number of positive numbers in the list. Call the function count_pos. Use variable num_pos
  count_pos(list,length);
  
  // Count the number of zeros in the list. Call the function count_zeros. Use variable num_zeros
  count_zeros(list,length);
  
  // Display number of positive elements
  cout << " Number of positive elements: " <<  num_pos << endl;
  
  // Display number of zeros
  cout << "Number of zero elements: " << num_zeros << endl;
  
  // De-allocate the list
 delete [] list;
  
  return 0;
}

// FUNCTION DEFINTIONS GO HERE
void get_list(int list[], int size) //This function has the user enter in values for the array
{
  int i(0); //Used for the while loop 
  int x(0); //Variable that the user enters

  cout << "Enter list: " << endl;

  while(i<size) //Fill in the elements with the corresponding locations
  {
    cin >> x;
    list[i]=x; //The spot in the list where the variable i is located is now filled in with x.
    i++; //Increase variable i by one to go to the next integer for list
  }

}

int count_pos(const int list[], int size) //This function counts how many positives are in the array
{
  int num_pos(0);
  for(int i=0; i < size; i++)
  {
    if(list[i]>0)
    {
      num_pos++;
    }
  }
}


int count_zeros(const int list[], int size) //This function counts how many zeros are in the array
{
  int num_zeros(0);
  for(int i=0; i < size; i++)
  {
    if(list[i] == 0)
    {
        num_zeros++;
    }
  }
}

I have fixed the code, but I am getting random numbers for the number of zeros and number of positive integers. How do I get it to display that without returning anything?

[thiskid]

I tried making num_pos and num_zeros a pointer but they still came up with randoms numbers. Still having trouble.