Segment Tree implementation in C++

SegmentTree.cpp

#include <iostream>
#include <math.h>
#include <vector>
#include <cstdio>
using namespace std;
#define RSUM 0
#define RMIN 1
#define RMAX 2

vector<int> mytree;
void init_tree(int n){
    int length = (int)(2*pow(2.0,floor((log((double)n)/log(2.0))+1)));
    mytree.resize(length,0);
}
void build(int code, int A[],int node, int beg, int end)
{
    if(beg == end)
    {
        if(code == RSUM) mytree[node] = A[beg];
        else             mytree[node] = beg;
    }
    else
    {
        int lndx = 2 * node, rndx = 2 * node +1;
        build(code, A, lndx, beg, (beg+end)/2);
        build(code, A, rndx, (beg+end)/2 + 1, end);
        
        int lcntnt = mytree[lndx], rcntnt = mytree[rndx];
        
        if(code == RSUM){mytree[node] = lcntnt + rcntnt;}
        else{
            int lval = A[lcntnt], rval = A[rcntnt];
            if (code == RMIN) mytree[node] = (lval <= rval) ? lcntnt : rcntnt;
            else mytree[node] = (lval >= rval) ? lcntnt : rcntnt;
        }
    }
}
int query(int code, int A[], int node, int b, int e, int i, int j) {
if (i > e || j < b) return -1; 
if (b >= i && e <= j) return mytree[node]; 

int p1 = query(code, A, 2 * node , b , (b + e) / 2, i, j);
int p2 = query(code, A, 2 * node + 1, (b + e) / 2 + 1, e , i, j);

if (p1 == -1) return p2; 
if (p2 == -1) return p1; 
if (code == RSUM) return p1 + p2;
else if (code == RMIN) return (A[p1] <= A[p2]) ? p1 : p2;
else return (A[p1] >= A[p2]) ? p1 : p2;
}


int main() {
	int n;
	cout << "Enter the no. of elements :\n";
	cin >> n;
    int A[n];
    init_tree(7); 
    cout << "Enter the elements : \n";
    for(int i = 0; i < n; i++)
    {
        cin >> A[i];
    }
    build(RMIN, A, 1, 0, n-1);
    int q, l, r;
    cout << "Enter no. of queries";
    cin >> q;
    while(q--)
    {
        cout << "Enter l and r " << endl;
        cin >> l >> r;
        printf("%d\n",query(RMIN, A, 1, 0, n-1, l, r) ); // answer
    }
    
    return 0;
}