一个类似于bc的计算器

***************************一个类似于bc的计算器，输入直接是表达式**********************





#include "stdio.h"
#include "string.h"
#include "stdlib.h"
#include "ctype.h"


void main( void )
{

 while(1)
 {
  char *inputs;
  char *str_left;
  char *str_right;

  int i;
  int flag = 0;
  int leftend;
  int rightend;
  int leftn = 0;
  int rightn = 0;
  int leftint;
  int rightint;
  int length = 1;
  int symbol;



  inputs = (char *)malloc( 100*sizeof( char) );
  if( inputs == NULL ) printf("init inputs error\n");
  str_left = ( char *)malloc( 10*sizeof( char) );
  if( inputs == NULL ) printf("init inputs error\n");
  str_right = ( char *)malloc( 10*sizeof( char ) );
  if( inputs == NULL ) printf("init inputs error\n");


  gets( inputs );

  for( i = 0; inputs[i] != 0; i++ )
  {
   if( inputs[i] == '+')
   {
    flag = i;
    symbol = 1;
   }
   if( inputs[i] == '-')
   {
    flag = i;
    symbol = 2;
   }
   if( inputs[i] == '*')
   {
    flag = i;
    symbol = 3;
   }
   if( inputs[i] == '/')
   {
    flag = i;
    symbol = 4;
   }
   if( i > 100 )
    printf("input error!!!");

   length ++;
  }



  for( i = 0; inputs[i] != 0; i++ )
  {
   if( i < flag && isdigit( inputs[i]) )
   {
     leftend = i;
     leftn++;
      str_left[leftn - 1] = inputs[i];

   }

   if( i > flag && isdigit( inputs[i]) )
   {
     rightend = i;
     rightn++;
     str_right[rightn - 1] = inputs[i];

   }
  }

  leftint = atoi(str_left);
  rightint = atoi(str_right);
  switch( symbol )
  {
   case 1: printf("%d\n", ( leftint + rightint )); break;
   case 2: printf("%d\n", ( leftint - rightint )); break;
   case 3: printf("%d\n", ( leftint * rightint )); break;
   case 4: printf("%lf\n", (double)( (double)leftint / (double)rightint )); break;
  }



  free( str_left );
  free( str_right );
  free( inputs );
 }

}