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;
}