将字符串转成整数以及整数转成字符串

1.将字符串转换成整数

           没什么难点，就是考虑的情况比较多。

#include<iostream>
#include<cctype>
#include<exception>
#include<climits>
#include<cstdio>
using namespace std;

long Str2Num(const char *str)
{
     if(!str)throw new std::exception("NULL String");
     bool isNegetive = false;
     int radix = 10;
     unsigned long ret = 0;
     if(*str == '-'){
	     isNegetive = true;
	     ++str;
     }else if(*str == '+')++str;
     if(*str == '0'&&(str+1)&&*(str+1)!='x'&&*(str+1)!='0'){
	     radix = 8;
	     ++str;
     }
     else if(*str == '0'&& tolower(*(str+1))=='x'){
	     radix = 16;
	     ++str;++str;
     }
     for(;*str!='';++str){
	     int ch = *str;
	     if((ch - '0') <radix){
	          ret = ret*radix + ch - '0';
         }
         else if(radix == 16 && ('a'<=tolower(ch)&&tolower(ch)<='f')){
	          ret = ret*radix + tolower(ch) - 'a' + 10;
         }
         else
	          throw new exception("Invalid num");
         if(ret>LONG_MAX)throw new exception("overfolw");
     }
     return isNegetive?(-ret):ret;
}

2.将整数转换成字符串（借用别人的，感觉还是有些情况没考虑到）

char * Num2Str(int Number)

{

   char ch,*str,*right,*left;

   unsigned int Value;

   str = (char *)malloc(12*sizeof(char));

   left = right = str;

   //如果是负数，则应加上负号，left、right向后走。

   if(Number < 0)

   {

      Value = -Number;

      *str = '-';

      left++,right++;

   }

   else

      Value = (unsigned)Number;

   //把数字转换成字符串（倒置的）

   while(Value)

   {

      *right = (Value%10)+0x30;

      Value = Value/10;

      right++;

   }

   *right-- = '';

   //把倒置的字符串正放过来

   while(right > left)

   {

      ch = *left;

       *left++ = *right;

       *right-- = ch;

   }

   return str;

}