binary tree using array

bt_array.cpp

#include<iostream>
#define SIZE 10
using namespace std;
char tree[SIZE];
void root(char key);
void set_left(char key, int parent);
void set_right(char key, int parent);
void display(void);
int main(){
    root('A');
    set_left('B', 0);
    set_right('C', 0);
    set_left('D', 1);
    set_right('E', 1);
    set_right('M', 3);
    display();
    return 0;
}
void root(char key){
    if(tree[0] != '\0')
        cout<<"tree already had root";
    else
        tree[0] = key;
}
void set_left(char key, int parent){
    if(tree[parent] == '\0')
        cout<<"No parent found at "<<(parent*2)+1;
    else
        tree[(parent*2)+1] = key;
}
void set_right(char key, int parent){
    if(tree[parent] == '\0')
        cout<<"No parent found at "<<(parent*2)+2;
    else
        tree[(parent*2)+2] = key;
}
void display(void){
    cout << "\n";
    for(int i = 0; i < 10; i++)
    {
        if(tree[i] != '\0')
            cout << tree[i];
        else
            cout << "-";
    }
    cout<<endl;
}