字符串与整数互转

#include <stdio.h>

// decimal to string
void dec_itoa(int num, char *str)
{
    int i=0,j=0;
    char temp[12];
    int n = num<0 ? -num:num;
    while(n)
    {
        temp[i++]=n%10+'0';
        n /=10;
    }
    temp[i]='\0'; /* 如是负数，留着放符号 */
    if(num>0) i--;
    while(i>=0)
        str[j++]=temp[i--];

    if(num<0)
        str[0]='-';
    str[j]='\0';
}

// sting to decimal int
int dec_atoi(const char *str)
{
    int x=0;
    int i,sign=1;
    while(*str==' ') str++;
    if(str[0]=='+'||str[0]=='-')
    {
        sign= (*str=='-'?-1:1);
    }
    else if( isdigit(str[0]) )
        x = str[0] - '0';
    for(i = 1; str[i] != '\0'; ++i)
    {
        if(str[i]>='0' && str[i]<='9')
            x=10*x + *str-'0';
    }
    return sign*x;
}

void main()
{
    char str[20];
    int n;
    printf("Please input an integer(-32767,32767):\n");
    scanf("%d",&n);
    dec_itoa(n,str);
    printf("output string: %s\n",str);

    printf("string to int: %d\n",dec_atoi(str));
}

// 把八、十、十六进制字符串转化成整数：

int StrToInt(char * str)
{
   int value = 0;
   int sign = 1;
   int radix;

   if(*str == '-')
   {
      sign = -1;
      str++;
   }
   if(*str == '0' && (*(str+1) == 'x' || *(str+1) == 'X'))
   {
      radix = 16;
      str += 2;
   }
   else if(*str == '0') // 八进制首字符为0
   {
      radix = 8;
      str++;
   }
   else
      radix = 10;

   while(*str)
   {
      if(radix == 16)
      {
        if(*str >= '0' && *str <= '9')
           value = value * radix + *str - '0';
        else
           value = value * radix + (*str | 0x20) - 'a' + 10;
       // 转化为小写字母
      }
      else
        value = value * radix + *str - '0';
      str++;
   }
   return sign*value;
}