Untitled

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

void insert(int *t, int key);
void preorder(int *t, int i);
int check(int *t, int i);
int main()
{
        int t[100];
        int i, ch, num, k;
        for(i = 0; i<100; i++)
        {
                t[i] = -1;
        }
        while(1)
        {
                printf("\n1. Insert\n2. Traverse\n3. Check\n4. Exit\n");
                printf("Enter your choice: ");
                scanf("%d", &ch);
                switch(ch)
                {
                        case 1: printf("\nEnter the number to insert: ");
                                scanf("%d", &num);
                                insert(t,num);
                                break;
                        
                        case 2: printf("Tree elements in preorder is: ");
                                preorder(t,0);
                                break;
                        
                        case 3: k = check(t,0);
                                if(k == 0)
                                {
                                        printf("\nIt is not a binary search tree\n");
                                }
                                else
                                {
                                        printf("\nIt is a binary search tree\n");
                                }
                                break;
                                
                        case 4: exit(0);
                }
        }
}

void insert(int *t, int key)
{
        int i = 0;
        while(t[i] != -1)
        {
                if(key < t[i])
                {
                        i = 2*i + 1;
                }
                else
                {
                        i = 2*i + 2;
                }
        }
        t[i] = key;
}

void preorder(int *t, int i)
{
        if(t[i] != -1)
        {
                printf("%d - ", t[i]);
                preorder(t, 2*i + 1);
                preorder(t, 2*i + 2);
        }
}

int check(int *t, int i)
{
        int n;
        if(t[i] != -1)
        {
                if(t[2*i + 2] == -1)
                {
                        check(t, 2*i + 1);
                }
                else if(t[2*i + 1] < t[i] && t[2*i + 2] > t[i])
                {
                        check(t, 2*i + 1);
                        check(t, 2*i + 2);
                }
                else
                {
                        return 0;
                }
        }
        else
        {
                return 1;
        }
}