c---string_to_double (atof)

#include

#include

#include

//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;

}