有关C++中的局部变量

返回的时候，如果局部变量是一个指针，返回的是局部变量的地址是会出错的。
因为返回的时候，这个局部变量已经消亡了，返回地址会是一片未知地址，造成麻烦。
解决办法：在函数中的局部变量前面加上static，成为静态变量。
具体例子：

#include <iostream> 
#include <cstring> 
#include <cstdlib> 
#include <cstdio> 
using namespace std;
const int MAX = 110;
class CHugeInt {
	int number[201];
public:
	CHugeInt(int n) {
		memset(number, 0, sizeof(number));
		int pos = 200;
		while ((n / 10) || (n % 10)) {
			number[pos] = n % 10;
			n /= 10;
			pos--;
		}
		//cout << *this;
	}
	CHugeInt(const char* w) {
		memset(number, 0, sizeof(number));
		int pos = 200;
		int posw = strlen(w) - 1;
		for (int i = posw; i >= 0; i--) {
			number[pos] = w[i] - '0';
			pos--;
		}
		//cout << *this;
	}
	CHugeInt(const CHugeInt &a) {
		for (int i = 200; i >= 0; i--) {
			number[i] = a.number[i];
		}
	}
	friend CHugeInt& operator+(const CHugeInt &nn, const CHugeInt &w) {
		static CHugeInt sum(0);
		int d = 0;
		int pos = 200;
		while (pos > 0) {
			d = d + nn.number[pos] + w.number[pos];
			sum.number[pos] = d % 10;
			d /= 10;
			pos--;
		}
		sum.number[pos] = d % 10;
		return sum;
	}
	CHugeInt& operator+=(int n) {
		CHugeInt nn(n);
		int d = 0;
		int pos = 200;
		while (pos > 0) {
			d = d + nn.number[pos] + number[pos];
			number[pos] = d % 10;
			d /= 10;
			pos--;
		}
		number[pos] = d % 10;
		return *this;
	}
	friend CHugeInt& operator+(CHugeInt& w,int n) {
		CHugeInt nn(n);
		static CHugeInt sum1(0);
		int d = 0;
		int pos = 200;
		while (pos > 0) {
			d = d + nn.number[pos] + w.number[pos];
			sum1.number[pos] = d % 10;
			d /= 10;
			pos--;
		}
		sum1.number[pos] = d % 10;
		return sum1;
	}
	friend CHugeInt& operator+(int n, CHugeInt& w) {
		CHugeInt nn(n);
		static CHugeInt sum2(0);
		int d = 0;
		int pos = 200;
		while (pos > 0) {
			d = d + nn.number[pos] + w.number[pos];
			sum2.number[pos] = d % 10;
			d /= 10;
			pos--;
		}
		sum2.number[pos] = d % 10;
		return sum2;
	}
	CHugeInt& operator++() {
		int pos = 200;
		number[pos] += 1;
		while (pos > 0) {
			number[pos - 1] += (number[pos] / 10);
			number[pos] %= 10;
			pos--;
		}
		return *this;
	}
	friend CHugeInt operator++(CHugeInt& w, int n) {
		CHugeInt temp(w);
		w += 1;
		return temp;
	}
	friend ostream& operator <<(ostream& cout, CHugeInt w) {
		int i0 = 0;
		for (int i = 0;; i++) {
			if (w.number[i]) {
				i0 = i;
				break;
			}
			if (i == 200) {
				i0 = i;
				break;
			}
		}
		for (int i = i0; i <= 200; i++) {
			cout << w.number[i];
		}
		return cout;
	}
	// 在此处补充你的代码
};

int  main()
{
	char s[210];
	int n;

	while (cin >> s >> n) {
		CHugeInt a(s); ////constructor（用大整数） 需要重载 
		CHugeInt b(n);
		cout << a + b << endl; ////重载+（两个对象） 
		cout << n + a << endl; ////重载+（对象和整数，满足交换律） 
		cout << a + n << endl;
		b += n;  ////重载+= 
		cout << ++b << endl; ////重载++i和i++ 
		cout << b++ << endl;   ////重载<< 
		cout << b << endl;
	}
	return 0;
}

在输出的时候，代码的a+b那一行在vs中输出了奇怪的东西，oj上是runtime error。在函数里面加cout答案是好的。返回的语句出了问题。当然我没在意那个warning，这样看起来re的线索可能在warning当中。在所有的sum前面加上了static并适当修改了变量名称就好了。