Writing a function with dynamic memory allocation in C

Question

I was trying to write a program that reads two arrays (and their sizes), writes the numbers that appear in both in a new array and returns the new array and it's size.

it throws me out after reading the arrays. I think I did a few things wrong with the dynamic memory allocation, still very confused by the whole thing.

I'd appreciate it if you could take a look and tell me what's wrong. thanks!

#include <stdio.h>
#include <stdlib.h>
int andArrays(int*, int*, int, int, int*);
void main()
{
    int size1, size2, i, j, s, num1, num2, newsize;
    printf("enter the size of the array >>> ");
    scanf_s("%d", &size1);
    int* arr1 = (int*) malloc(size1*sizeof(int));
    printf("enter %d numbers: ", size1);
    for (i = 0; i < size1; i++)
    {
        scanf_s("%d\n", &num1);
        arr1[i] = num1;
    }
    printf("enter the size of the array >>> ");
    scanf_s("%d", &size2);
    int* arr2 = (int*)malloc(size2*sizeof(int));
    printf("enter %d numbers: ", size2);
    for (j = 0; j < size1; j++)
    {
        scanf_s("%d\n", &num2);
        arr2[j] = num2;
    }
    int newarray = andArrays(&arr1, &arr2, size1, size2, &newsize);
    printf("size of new array is: %d", newsize);
    for (s = 0; s < newsize; s++)
        printf("%d", newarray[s]);
    free (newarray);
    free(arr1);
    free(arr2);
}

int andArrays(int* arr1, int* arr2, int size1, int size2, int* newsize)
{
    int i = 0, j = 0, num, f = 0;
    int* newarr = (int*)malloc(size1 * sizeof(int));
    while (1)
    {
        if (arr1[i] == arr2[j])
        {
            num = arr1[i];
            newarr[f] = num;
            f++;
        }
        i++;
        j++;
        if (i == size1)
            break;
    }
    *newsize = f;
    }
}

I did accidently put andArrays in the main at first but it isn't anymore — user14928249
– user14928249, Commented Jan 7, 2021 at 19:18

Nishad C M · Accepted Answer · 2021-01-07 19:21:36Z

2

Issue is with second read loop, the value is read for "size2", but the for loop is check for "size1".

    scanf_s("%d", &size2);
    int* arr2 = (int*)malloc(size2*sizeof(int));
    printf("enter %d numbers: ", size2);
    for (j = 0; j < size1; j++)   >>>> for (j = 0; j < size2; j++)
    {
        scanf_s("%d\n", &num2);
        arr2[j] = num2;
    }

also the function "andArrays" should return a array of integers, not one single int.

    int andArrays(int*, int*, int, int, *int);   >>>>>   int * andArrays(int*, int*, int, int, int*); //declaration of function

code:

    #include <stdio.h>
    #include <stdlib.h>
    int * andArrays(int*, int*, int, int, int*); //declaration of function
    int main ()
    //void main()
    {
        int size1, size2, i, j, s, num1, num2, newsize;
        printf("enter the size of the array >>> ");

        scanf("%d", &size1);
        int* arr1 = (int*) malloc(size1*sizeof(int));

        printf("\nenter %d numbers: ", size1);

        for (i = 0; i < size1; i++)
        {
            scanf(" %d", &num1);
            arr1[i] = num1;
        }
        printf("\nenter the size of the array >>> ");
        scanf(" %d", &size2);

        int* arr2 = (int*)malloc(size2*sizeof(int));
        printf("\nenter %d numbers: ", size2);

        for (j = 0; j < size2; j++)
        {
            scanf(" %d", &num2);
            arr2[j] = num2;
        }

        int * newarray = andArrays(arr1, arr2, size1, size2, &newsize);
        printf("\nsize of new array is: %d\n Array : ", newsize);
        for (s = 0; s < newsize; s++)
            printf(" %d ", newarray[s]);
        //free (newarray);
        //free(arr1);
        //free(arr2);
        printf("\n");
        return 0;
    }
    int * andArrays(int* arr1, int* arr2, int size1, int size2, int* newsize)
    {
        int i = 0, j = 0, num, f = 0;
        int* newarr = (int*)malloc(size1 * sizeof(int));
        while (1)
        {
            if (arr1[i] == arr2[j])
            {
                num = arr1[i];
                newarr[f] = num;
                f++;
            }
            i++;
            j++;
            if (i == size1)
                break;
        }
        *newsize = f;
        return newarr;
    }

answered Jan 7, 2021 at 19:21

Nishad C M

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3 Comments

user14928249 Over a year ago

Thank you for your help! it still doesn't seem to work when the new array is more than two numbers...

Nishad C M Over a year ago

please update your latest code in question. make sure size1 and size2 are used correctly. have you tried with the code which i hv shared ?

Nishad C M Over a year ago

NISM-M-9168:dirtest nism$ ./a.out enter the size of the array >>> 4, enter 4 numbers: [1 2 3 4] enter the size of the array >>> 5, enter 5 numbers: [1 2 3 4 5] size of new array is: 4, Array : [1 2 3 4]

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