谁能告诉我这是为什么呢？C++变量初始化问题

	public static void main(String[] args) {
		int num = 50, total = 0;
		while (num <= 100) {
			total += num;
			num++;
		}
		System.out.println("total=" + total);
		int val = 0;
		for (int i = 50; i <= 100; i++) {
			val += i;
		}
		System.out.println("val=" + val);
	}

java里这个for和while的结果是相同的，但是在C++里，结果就不一样了！

#include <iostream>
using namespace std;
int main() {
	cout << "this is demo" << endl;
	int num = 50, total;
	while (num <= 100) {
		total += num;
		++num;
	}
	cout << "50到100相加的和是：" << total << endl;
	int val;
	for (int i = 50; i <= 100; ++i) {
		val += i;
	}
	cout << "again..." << val << endl;

	return 0;
}