这段代码有什么问题并纠正：#define _CRT_SECURE_NO_WARNINGS #include<iostream> #include<stdio.h> using namespace std; const int MAXN = 50010; int T, N; int a[MAXN], tree[MAXN*4]; void build(int node, int l, int r) { if (l == r) { sum[node] = a[r]; return; } int mid = (r - l) / 2 + l; build(node * 2, l, mid); build(node * 2 + 1, mid + 1, r); sum[node] = sum[node * 2] + sum[node * 2 + 1]; } void update(int node, int l, int r, int x, int v) { if (l == r) { sum[node] += v; return; } int mid = (l + r) >> 1; if (x <= mid) update(node * 2, l, mid, x, v); else update(node * 2 + 1, mid + 1, r, x, v); sum[node] = sum[node * 2] + sum[node * 2 + 1]; } int query(int node, int l, int r, int ql, int qr) { if (ql <= l && qr >= r) return sum[node]; int mid = (l + r) >> 1, res = 0; if (ql <= mid) res += query(node * 2, l, mid, ql, qr); if (qr > mid) res += query(node * 2 + 1, mid + 1, r, ql, qr); return res; } int main() { int T,n=0; cin >> T; while(T--){ int N; cin >> N; n++; cout << "Case " << n << ":" << endl; for (int i = 1; i <= N; ++i) { cin >> a[i]; } build(1, 1, N); char op[5]; while (1) { cin >> op; if (op[0] == 'E') break; if (op[0] == 'A') { int x, i; cin >> x >> i; update(1, 1, N, i, x); } else if (op[0] == 'S') { int x, i; cin >> x >> i; update(1, 1, N, i, -x); } else { int i, j; cin >> i >> j; printf("%d\n", query(1, 1, N, i, j)); } } } return 0; }

有两个问题：
1. 在函数 build 中，变量名 sum 是未定义的；
2. 在主函数中，已经定义了全局变量 T，但在 while 循环中又重新定义了局部变量 T。

纠正后的代码如下：

#define _CRT_SECURE_NO_WARNINGS
#include<iostream>
#include<stdio.h>
using namespace std;

const int MAXN = 50010;

int T, N;
int a[MAXN], sum[MAXN*4];

void build(int node, int l, int r) {
    if (l == r) {
        sum[node] = a[r];
        return;
    }
    int mid = (r - l) / 2 + l;
    build(node * 2, l, mid);
    build(node * 2 + 1, mid + 1, r);
    sum[node] = sum[node * 2] + sum[node * 2 + 1];
}

void update(int node, int l, int r, int x, int v) {
    if (l == r) {
        sum[node] += v;
        return;
    }
    int mid = (l + r) >> 1;
    if (x <= mid)
        update(node * 2, l, mid, x, v);
    else
        update(node * 2 + 1, mid + 1, r, x, v);
    sum[node] = sum[node * 2] + sum[node * 2 + 1];
}

int query(int node, int l, int r, int ql, int qr) {
    if (ql <= l && qr >= r)
        return sum[node];
    int mid = (l + r) >> 1, res = 0;
    if (ql <= mid)
        res += query(node * 2, l, mid, ql, qr);
    if (qr > mid)
        res += query(node * 2 + 1, mid + 1, r, ql, qr);
    return res;
}

int main() {
    cin >> T;
    for (int n = 1; n <= T; ++n) {
        cin >> N;
        cout << "Case " << n << ":" << endl;
        for (int i = 1; i <= N; ++i) {
            cin >> a[i];
        }
        build(1, 1, N);
        char op[5];
        while (1) {
            cin >> op;
            if (op[0] == 'E') break;
            if (op[0] == 'A') {
                int x, i;
                cin >> x >> i;
                update(1, 1, N, i, x);
            }
            else if (op[0] == 'S') {
                int x, i;
                cin >> x >> i;
                update(1, 1, N, i, -x);
            }
            else {
                int i, j;
                cin >> i >> j;
                printf("%d\n", query(1, 1, N, i, j));
            }
        }
    }
    return 0;
}