C++  函数atoi,itoa 的实现

 #include "stdafx.h"

#include <iostream>

using namespace std;

void itoaTest(int num,char str[] )

{

int sign = num,i = 0,j = 0;

char temp[11];

if(sign<0)//判断是否是一个负数

{

num = -num;

};

do

{

temp[i] = num%10+'0';

num/=10;

i++;

}while(num>0);

if(sign<0)

{

temp[i++] = '-';

}

temp[i] = '\0';

i--;

while(i>=0)

{

str[j] = temp[i];

j++;

i--;

}

str[j] = '\0';

}

 int atoiTest(char s[])

{

int i = 0,sum = 0,sign; //输入的数前面可能还有空格或制表符应加判断

while(' '==s[i]||'\t'==s[i])

{

i++;

}

sign = ('-'==s[i])?-1:1;

if('-'==s[i]||'+'==s[i])

{

i++;

}

while(s[i]!='\0')

{

sum = s[i]-'0'+sum*10;

i++;

}

return sign*sum;

}