VS2008与DEV C++的区别

[xiaoshi935]

运行了一个程序，发现在DEV下可以运行，而拿到VS2008下提示如下错误，真是莫名其妙：
“<”: 有符号/无符号不匹配
error C2057: 应输入常量表达式
error C2466: 不能分配常量大小为 0 的数组
error C2133: “numResult”: 未知的大小
error C2057: 应输入常量表达式
error C2466: 不能分配常量大小为 0 的数组
error C2133: “numResult”: 未知的大小

程序如下：

/*
 * exe1102.cpp
 * 用类的方法进行求解下题
 * 
 * A + B Problem
 *
 * Input
 * The input will consist of a series of pairs of integers a and b, separated by one line. 
 * Each integer may consist of less than 79 digits.
 *
 * Output
 * For each pair of input integers a and b you should output the sum of a and b in one line
 *
 * Sample input
 * 1
 * 5000000000000000000000000000000000000000000000000000000000
 * -1
 * 23
 *
 * Sample output
 * 5000000000000000000000000000000000000000000000000000000001
 * 22
 */

#include <iostream>
#include <fstream>
#include <string>
using namespace std;

class BigInt {  //定义大整数类
  string s; 
  int sign;
public:
  BigInt (const string &num);
  BigInt (int sign, const string &value);
  ~BigInt () {}
  static string numberArrayToString (int a[], int length);
  static int numValueCompare (const string &a, const string &b);
  string getNumValue () { return s; };
  int getSign () { return sign; }
  friend BigInt operator + (const BigInt a, const BigInt b); //重载操作符+
  // Pre-Condition: a >= b >= 0
  friend BigInt operator - (const BigInt a, const BigInt b); //重载操作符- 
  friend ostream &operator << (ostream &o, const BigInt &a); //重载输出操作符
};

BigInt::BigInt (const string &num) {
  if (num[0] == '-') {
    sign = -1;
    s = num.substr( 1);
  } else {
    sign = 1;
    s = num;
  }
}

BigInt::BigInt (int sign, const string &value) {
  this->sign = sign;
  s = value;
}
  
string BigInt::numberArrayToString (int a[], int length) {
  string result = "";
  int i = 0;
  while (i < length-1 && a[i] == 0)
    ++i;
  while (i < length) {
    result += (char)(a[i] + '0');
    ++i;
  }
  return result;
}
   
int BigInt::numValueCompare (const string &a, const string &b) {
  if (a.size() < b.size()) return -1;
  if (a.size() > b.size()) return 1;

  for (int i= 0; i < a.size(); ++i) {
    if (a[i] < b[i]) return -1;
    if (a[i] > b[i]) return 1;
  }      
  return 0;
} 
   
// Pre-Condition: a >= b >= 0
BigInt operator - (const BigInt a, const BigInt b) {
  int shortLen = b.s.size();
  int longLen  = a.s.size();
  string shortNum = b.s;
  string longNum  = a.s;

  int numResult[longLen];
    
  int temp, i, j;
  int rent = 0;
  for (i= longLen-1, j= shortLen-1; i >= 0 && j >= 0; i--, j--) {
    temp = (longNum[i] - '0') - (shortNum[j] - '0') - rent;
    rent = ((temp < 0) ? 1 : 0);
    numResult[i] = temp + rent * 10;
  }
  
  while (i >= 0) {
    temp = (longNum[i] - '0') - rent;
    rent = ((temp < 0) ? 1 : 0);
    numResult[i] = temp + rent * 10;
    --i;
  } 

  return BigInt( 1, BigInt::numberArrayToString( numResult, longLen));
} 

BigInt operator + (const BigInt a, const BigInt b) {
  if (a.sign == b.sign) {
    int shortLen, longLen;
    string shortNum, longNum;
    if (a.s.size() <= b.s.size()) {
      shortLen = a.s.size();
      longLen  = b.s.size();
      shortNum = a.s;
      longNum  = b.s;
    } else {
      shortLen = b.s.size();
      longLen  = a.s.size();
      shortNum = b.s;
      longNum  = a.s;
    }
  
    int numResult[longLen+1];
  
    int temp, i, j;
    int carry = 0;
    for (i= longLen-1, j= shortLen-1; i >= 0 && j >= 0; i--, j--) {
      temp = longNum[i] - '0' + shortNum[j] - '0' + carry;
      numResult[i+1] = temp % 10;
      carry = temp / 10;
    }
    while (i >= 0) {
      temp = longNum[i] - '0' + carry;
      numResult[i+1] = temp % 10;
      carry = temp / 10;
      i--;
    }
    numResult[0] = carry;
    return BigInt( a.sign, BigInt::numberArrayToString( numResult, longLen+1));
  }
  
  // now a and b in different sign
  int compareResult = BigInt::numValueCompare( a.s, b.s );
  if (compareResult == 0)
    return BigInt( 1, string( "0" ));
  if (compareResult < 0) 
    return BigInt( b.sign, (BigInt( 1, b.s) - BigInt( 1, a.s)).getNumValue());
  if (compareResult > 0) 
    return BigInt( a.sign, (BigInt( 1, a.s) - BigInt( 1, b.s)).getNumValue());
}

ostream &operator << (ostream &o, const BigInt &a) {
  return o <<(a.sign == -1 ? "-" : "") <<a.s;
}

int main () {
	BigInt a("500000000000000000009999999");
	BigInt b("600000000000000000009999999");
	cout << a + b << endl;
	BigInt c("-500000000000000000009999999");
	BigInt d("600000000000000000009999999");
	cout << c + d << endl;
}

其实也就是那个BigInt operator - 和BigInt operator + 里面的数组 int numResult[longLen]和 int numResult[longLen+1]的问题。
通过这个程序感觉好像VS2008好像一个成员函数中定义数组之前必须分配大小，而不是参数的大小，比方此题中的longLen = a.s.size();
这个究竟是什么问题呢，该怎么改呢？

[lingyin55]

int numResult[longLen];
不是动态定义的数组在编译期间就要求知道数组的大小。

[taodm]

哎，定义数组要用常量。c++9标准就这么规定了的。基础呀。

[lingyin55]

for (unsigned int i= 0; i < a.size(); ++i) {////这里把i定义成unsigned就行
if (a[i] < b[i]) return -1;
if (a[i] > b[i]) return 1;
}

[lingyin55]

vs2008对于类型匹配的检查相对其它编译器都要严格。

[fox000002]

lz 在无意中用了编译器的扩展

但是不是每个编译器都吃这一套

[Kusk]

C99支持动态长度数组，但C＋＋标准不支持。

[fairchild811]

vs2008支持的标准一些.devcpp老了,好像好久没更新了

[s510601017]

cv2008是安C#编辑器，不是VC6.0的标准。

[Sou2012]

MARK!!

[amossavez]

进来看看！

[sandy_zc_1]

DevCpp用的是GCC的编译器，GCC编译器符合GNU C++的标准，但是不一定完全符合C++语言的规范。LZ的问题就是使用了GCC提供的一些扩展特性，而标准C++是不支持这个东西的。

这种动态的数组大小，应该用new分配，用完了再用delete回收。