#include <stdio.h>
#include <string.h>
#include <ctype.h>
//将字符串转换为浮点数
double atof(char *a)
{
int sign = 1;
//此处3个变量必须赋值为double型变量
double digit = 0.0;
double decimal = 0.0;
double power = 10.0;
int i = 0;
//开始循环遍历字符串，依次遇到 空格，数字，小数点，数字，则开始转换
for(; isspace(a[i]) ; i ++)
{
;
}
switch(a[i])
{
case '+':
i ++;
break;
case '-':
sign = -1;
i ++;
break;
default:
break;
}
for(; isdigit(a[i]); i ++)
{
digit = digit * 10 + a[i] - '0';
}
if(a[i] == '.')
{
i ++;
}
for(; isdigit(a[i]); i ++)
{
//a[i] - '0' 即将字符转为数字，此处为int型
decimal = decimal + (a[i] - '0') / power;
power *= 10;
}
return sign * (digit + decimal);
}
int main(int argc,char *argv[])
{
char a[20] = " -123.345";
double ax = 0;
ax = atof(a);
printf("%lf",ax);
return 0;
}
