各位帮忙找一下哪出错了。

我跟着书上编的，这是一个计算器，可以计算+ - * / 还有^。可以使用前一个计算的结果进行计算。我编译后运行了，但只能计算整数的，有小数的就乱了。

#include <stdio.h>
#include <string.h>
#include <ctype.h>
#include <stdlib.h>
#include <math.h>
#define BUFFER_LEN 256
int main(void)
{
char input[BUFFER_LEN];
char number_string[30];
char op = 0;
unsigned int index = 0;
unsigned int to = 0;
size_t input_length = 0;
unsigned int number_length = 0;
double result = 0.0;
double number = 0.0;
printf("\nTo use this calculater, enter any expression with"
"or without spaces");
printf("\nAn expression may include the operators:");
printf("\n +, -, *, /, %%, or ^(raise to a power).");
printf("\nUse = at the beginning of a line to operate on ");
printf("\nthe result of the previous calculation.");
printf("\nUse qyit by itself to stop the clculator,\n\n");
while(strcmp(fgets(input, BUFFER_LEN, stdin), "quit\n") != 0)
{
input_length = strlen(input); i
nput[--input_length] = '\0';
for(to = 0, index = 0 ;index<=input_length ; index++)
if(*(input+index) != ' ')
*(input+to++) = *(input+index);
input_length = strlen(input);
index = 0;
if(input[index]== '=') index++;
else
{
number_length = 0;
if(input[index]=='+' || input[index]=='-')
*(number_string+number_length++) = *(input+index);
for( ; isdigit(*(input+index)) ; index++)
*(number_string+number_length++) = *(input+index);
if(*(input+index)=='.')
{
*(number_string+number_length) = *(input+index++);
for( ; isdigit(*(input+index)) ; index++)
*(number_string+number_length++) = *(input+index);
}
*(number_string+number_length) = '\0';
if(number_length>0) result = atof(number_string);
}
for(;index < input_length;)
{
op = *(input+index++); number_length = 0;
if(input[index]=='+' || input[index]=='-')
*(number_string+number_length++) = *(input+index++);
for( ; isdigit(*(input+index)) ; index++)
*(number_string+number_length++) = *(input+index);
if(*(input+index)=='.')
{
*(number_string+number_length++) = *(input+index++);
for( ; isdigit(*(input+index)) ; index++)
*(number_string+number_length++) = *(input+index);
}
*(number_string+number_length) = '\0';
number = atof(number_string);
switch(op)
{
case '+': result += number; break; case '-':
result -= number;
break;
case '*':
result *= number;
break;
case '/':
if(number == 0)
printf("\n\n\aDivision by zero error!\n");
else result /= number;
break; case '%':
if((long)number == 0)
printf("\n\n\aDivision by zero error!\n");
else result = (double)((long)result % (long)number);
break;
case '^':
result = pow(result, number);
break; default:
printf("\n\n\aIllegal operation!\n");
break;
}
}
printf("= %lf\n", result);
}
return 0;
}
代码有点乱啊，因为书了的注释是英语的，所以我没有写注释，对这个程序我也不是很懂，有空的高手就帮一下忙。

代码这么长，谁有那个时间看啊，还是自己对照着书上的解释把代码弄明白才行！

http://training.tsinghua.edu.cn