itoa与atoi ftoa与atof的实现

     itoa与atoi ，有的系统库中有提供这两个函数的实现，前两天也自己尝试写写这两个函数，代码实现如下：

 

     /*============itoa=============*/

     /*把num转换成字符串存放在str 指向的字符串里*/

 

     int myitoa(int num, char *str)

     {

          int temp;

          int sign = 0;                          //标记num的符号

 

          char *p;

 

          if (str == NULL)    return -1;

 

          p = str;

 

          /*负数的话取绝对值并改变标记*/

          if (num < 0)

          {

                     num = 0 - num;

                     sign = 1;

          }

 

          /*把数从低位放进字符串*/

          do

          {

                     temp = num % 10;    //取num的最后一位

                     *(p++) = temp + '0';

 

          }while ((num /= 10) != 0);

 

          /*是负数的时候添加‘-’*/

          if (sign == 1)

          {

                    *(p++) = '-';

          }

 

           /*给字符串的末尾添加 ''/0*/

          *(p+1) = '/0';

 

 

          /*字符串逆置*/

          while(str < p)

          {
                   *str = *str + *p;

                   *p = *str - *p;

                   *str = *str - *p;

 

                   str++;

                   p--;

          }

 

 

          return 0;

 

      }

 

 

 

 

      /*========atoi========*/

      /*把str指向的字符串转换成数字*/

 

      #include <stdlib.h>

 

      int myatoi(const char *str)

      {

           int sum = 0;

           int sign = 0;

 

           if (str == NULL)

           {

                    perror("The string is NULL!/n");

                    exit(-1);

           }

 

           /*判断是否为负数*/

           if (*str == '-')

           {

                    sign = 1;

                    str++;

           }

 

 

           /*转换*/

           while (*str != '/0')

           {

                     sum = 10*sum + (*str - '0');

                     str++;

           }

 

 

            /*判断是否为负数*/

           if(sign == 1)

           {

                    sum = 0 - sum;

           }

 

           return sum;

 

      }

 

      另外还写 float 与 字符串 转换，代码如下

 

     

/*
 *File : ftoa.c
 */

/*Float ===> String*/

int ftoa(char *str, float num, int n)        //n是转换的精度，即是字符串'.'后有几位小数
{
    int     sumI;
    float   sumF;
    int     sign = 0;
    int     temp;
    int     count = 0;

    char *p;
    char *pp;

    if(str == NULL) return -1;
    p = str;

    /*Is less than 0*/
    if(num < 0)
    {
        sign = 1;
        num = 0 - num;
    }

    sumI = (int)num;    //sumI is the part of int
    sumF = num - sumI;  //sumF is the part of float

    /*Int ===> String*/
    do
    {
        temp = sumI % 10;
        *(str++) = temp + '0';
    }while((sumI = sumI /10) != 0);

    /*******End*******/

 

    if(sign == 1)
    {
        *(str++) = '-';
    }

    pp = str;
   
    pp--;
    while(p < pp)
    {
        *p = *p + *pp;
        *pp = *p - *pp;
        *p = *p -*pp;
        p++;
        pp--;
    }

    *(str++) = '.';     //point

    /*Float ===> String*/
    do
    {
        temp = (int)(sumF*10);
        *(str++) = temp + '0';

        if((++count) == n)
            break;
   
        sumF = sumF*10 - temp;

    }while(!(sumF > -0.000001 && sumF < 0.000001));

    *str = '/0';

    return 0;

}

 

 

/*
 * File : atof.c
 */

/*String ===> Float*/

float atof(const char *str)
{
    float   sumF = 0;
    int     sumI = 0;
    int     sign = 0;

    if(str == NULL) return -1;
   
    /*Is less than 0 ?*/
    if(*str == '-')
    {
        sign = 1;
        str++;
    }

    /*The part of int*/
    while(*str != '.')
    {
        sumI = 10*sumI + (*str - '0');
        str++;
    }

    /*Let p point to the end*/
    while(*str != '/0')
    {
        str++;
    }

    str--;          //Your know!

    /*The part of float*/
    while(*str != '.')
    {
        sumF = 0.1*sumF + (*str - '0');
        str--;
    }

    sumF = 0.1*sumF;

    sumF += sumI;

    if(sign == 1)
    {
        sumF = 0 - sumF;
    }

    return sumF;

}
 

    

 

 

 

 

以上的代码简单测试通过，可能写得很粗糙，健壮性不是很好，若有什么地方不足或不对，欢迎指出！