Convert a string to an integer or an integer to a string.

1. Convert the string to an integer

There is no difficulty, that is, there are many situations to consider.

 

#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!='\0';++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; } #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!='\0';++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; 

Char * Num2Str (int Number) {char ch, * str, * right, * left; unsigned int Value; str = (char *) malloc (12 * sizeof (char )); left = right = str; // if it is a negative number, a negative number should be added, and left and right should go backward. If (Number <0) {Value =-Number; * str = '-'; left ++, right ++;} else Value = (unsigned) Number; // convert the number into a string (inverted) while (Value) {* right = (Value % 10) + 0x30; Value = Value/10; right ++ ;} * right -- = '\ 0'; // put the inverted string in front while (right> left) {ch = * left; * left ++ = * right; * right -- = ch;} return str ;}