Wrong Output in linked list in C

Question

In my code, I have to do compare two list, one of them should be dynamic array, another should be linked list. so I wrote something like this; Specially I do not sure for this function

node * insert(node *head, int num){
    node *new = (node *) malloc(sizeof(node));
    new->data = num;
    new->next = NULL;

    //if head is null execute
    if (head == NULL){
        head = new;
    } 
    else{
        node *current = head;

        while (current->next != NULL){
            current = current->next;
        }
        current->next = new;
    }

    return head;
}

And my whole code down below

#include <stdio.h>
#include <stdlib.h> 

typedef struct nodes {
    int data;
    struct nodes * next;
}node;

typedef struct differents{
    int n1,n2;
}different;

node * insert(node *head, int num);
different * compare(node *head, int * arr,int counter, int *count_dif);
void print_arr(int *arr,int counter);
void print_linked(node *head);

int main(){
    int *arr,*temp;
    node *head=NULL;
    int counter=1,input,count_dif;
    different *dif;


    arr=(int*)malloc(sizeof(int));
    printf("'0' for stop entering new number\n");
    while (input !=0){
        printf("Input:");
        scanf(" %d",&input);
        arr[counter-1]=input;
        counter++;
        temp=arr;
        arr=(int*)calloc(counter,sizeof(int));
        for (int i=0; i<counter-1; i++) arr[i]=temp[i];

        free(temp);
    }
    counter-=2;
    printf("You are entered %d num for the first list\nEnter %d num for the second list\n",counter,counter );

    for (int i=0; i<counter; i++){
        printf("Input:");
        scanf(" %d",&input);
        head=insert(head,input);
    }

    print_arr(arr,counter);

    print_linked(head);


    node *temp_head=head;
    dif=compare(temp_head,arr,counter,&count_dif);

    printf("There are %d different num in the lists\nThey are\nIn first list\tIn second list\n",count_dif );
    for (int i=0; i<count_dif; i++){
        printf("\t%d\t\t",dif[i].n1 );
        printf("%d\n",dif[i].n2 );

    }



}

node * insert(node *head, int num){
    node *new = (node *) malloc(sizeof(node));
    new->data = num;
    new->next = NULL;

    //if head is null execute
    if (head == NULL){
        head = new;
    } 
    else{
        node *current = head;

        while (current->next != NULL){
            current = current->next;
        }
        current->next = new;
    }

    return head;
}

different * compare(node *head, int * arr,int counter, int *count_dif){
    different *dif,*temp;
    int diff_num=1;

    for (int i=0; i<counter; i++){
        if (arr[i]!=head->data){
            temp=dif;
            dif=(different*)calloc(diff_num,sizeof(different));
            for (int j=0; j<diff_num; j++) dif[j]=temp[j];
            dif[diff_num-1].n1=arr[i];
            dif[diff_num-1].n2=head->data;
            if (temp!=NULL) free(temp);
            diff_num++;
        }

        head=head->next;
    }

    *count_dif=diff_num-1;
    return dif;
}

void print_arr(int *arr,int counter){
    printf("first  list:{ ");
    for (int i=0; i<counter; i++) printf("%d ",arr[i] );
    printf("}\n");
}

void print_linked(node *head){
    printf("second list:{ ");
    node *print=head;
    while(print){
        printf("%d ",print->data );
        print=print->next;
    }printf("}\n");
}

INPUT

5 4 6 3 0
5 2 4 3

Expected OUTPUT

first  list:{ 5 4 6 3 }
second list:{ 5 2 4 3 }
There are 2 different num in the lists
They are
In first list   In second list
        4               2
        6               4

OUTPUT

first  list:{ 5 4 6 3 }
second list:{ 5 2 4 3 }
There are 2 different num in the lists
They are
In first list   In second list
        4               2
        6               -281779616

If I enter more than 6 or 7 number, It works fine, But in little numbers, It gives me a garbage value.

Answer 1

1. Use of uninitialized variables.

In main the variable input isn't initialized but it's used like: while (input !=0){ before any assignment.

In compare the variable dif isn't initialized but it's used like: temp=dif; before any assignment.

2. Out of bounds access

This code: for (int j=0; j<diff_num; j++) dif[j]=temp[j]; makes you access temp out of bounds.

You probably want:

for (int j=0; j<diff_num-1; j++) dif[j]=temp[j];
                        ^^

That said, you should really study what realloc can do for you. Your code will be much easier to read and without the "copying bug".