returning an array address from function in c++ issue

Question

i'm new to programming , this code gives me syntax error in line => int *result = apply_all(array1,5,array2,3) this is the error: expected primary-expression before '}' token|
i'm trying to write function called apply_all expects 2 arrays of integers and their sizes and dynamically allocates a new array of integers whose size is the product of 2 array sizes. the function should loop through the 2nd array and multiple each element accross each element of array 1 and store the product in newly created array. the function is returning a pointer of to the newly allocated array. also i wrote a function which is print to display the 1st & 2nd & newly array.

#include <iostream>

using namespace std;
//function prototype
int *apply_all(int *array1 ,int size1,int *array2,int size2);
void print(int *array,int size);



int main()
{
    int array1[] {1,2,3,4,5};
    int array2[] {10,20,30};

    cout << "Array 1:";
    print(array1,5);

    cout << "Array 2:";
    print(array2,3);

    int *result = apply_all(array1,5,array2,3);             
    cout << "Result : ";
    print(result,15);
    delete [] result;
    return 0;
}


int *apply_all(int *array1 ,int size1,int *array2,int size2)
{
        int *result {nullptr};
        result = new int[size1 * size2];   
        for (int i{0};i<size2;i++)          
            for(int j{0};j<size1;j++)          
                  *(result[i*5+j]) = *(array1[i])**(array2[j]);           
        return result;
}


void print(int *array,int size)
{
    for(auto num:array)
        cout << num << endl;
}

also i was thinking to replace this line *(result[i*5+j]) = *(array1[i])**(array2[j]); to be *(result++) = *array1[i]**array2[j]; or create a new variable for ex: k++ in for loop and *(result[k]) = *array1[i]**array2[j]; — logan_92
– logan_92, Commented Jul 3, 2020 at 19:48

cigien · Accepted Answer · 2020-07-03 20:03:15Z

2

On this line:

*(result[i*5+j]) = *(array1[i])**(array2[j]);

since result[i*5+j] gives you an int, you are trying to dereference an int, which is not possible.

You just need to do:

result[i*5+j] = array1[i] * array2[j];

Also, in print, your range-for loop won't work with a pointer. You need to do:

for(int i = 0; i < size; ++i)
    cout << array[i] << endl;

Also, in apply_all, your loop bounds are incorrect. i needs to go till size1, and j needs to go to size2.

Here's a demo.

edited Jul 3, 2020 at 20:03

answered Jul 3, 2020 at 19:49

cigien

61.2k11 gold badges86 silver badges124 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

logan_92 Over a year ago

thank you so much but i have 2 questions 1- *(result[i*5+j]) = *(array1[i])**(array2[j]); , so this line i've already accessed the array elements because i use array subscript notation [] so i don't need to deference it?? what i understand result now has the address of array in heap. so to access it i can use [] or * 2- why range-for loop won't work with a pointer?? sorry for those beginner questions

cigien Over a year ago

Yes, [] and * are related like you say. For the second question see stackoverflow.com/questions/15904896/…

logan_92 Over a year ago

thank you :) i read that in the article you provided You can't use range-for-loop with dynamically allocated arrays, since compiler can't deduce begin and end of this array can i use vector with pointer in for range based??? void display (vector<string> *v) { for(auto str: *v) cout << str << endl;} int main(){ vector<string> str1 ["joe","logan","Jasmine"] display(&str1);

cigien Over a year ago

You could, but just pass in the vector by reference, instead of by pointer.

pleb_coder72 · Accepted Answer · 2020-07-03 20:13:52Z

Since you are new, a simple work around would be creating an array with buffer space to store your results in and passing the pointer for this into apply_all. You could then write to this array which (being declared in main) should be very easy to access and cause few errors and use a c-string like ending to know when your results are over and to stop printing from the array (c-strings end with a value of 0 so that programs don't read unrelated memory). eg:

int buf[99];
apply_all(array_1, size1, array_2, size2, buf, size3);
for (int x = 0; buf[x] != end of buf var; x++;)
{
    print(buf[x])
}

and

apply_all()
{
    buf[start-end] = whatever you want;
    buf[end + 1] = some variable that won't appear in buffer; //max int size?
}

Collectives™ on Stack Overflow

returning an array address from function in c++ issue

2 Answers 2

4 Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

4 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related