calc.c

运行于T-Engine(使用T-Kernel操作系统)的实例源码

/*
 * calc.c - a very small calculator.
 *
 * Copyright (C) YRP Ubiquitous Networking Laboratory, 2005.
 */

#include <basic.h>
#include <stdio.h>
#include <tk/tkernel.h>

typedef enum {
  OP_NOP,
  OP_PLUS,
  OP_MINUS,
  OP_MUL,
  OP_DIV
} CalcOp;

/*
 * A very small calculator.
 * It accepts only the following formula:
 *   <number1><op><number2>
 * where
 *     <number1>        an arbitrary decimal number
 *     <op>             '+', '-', '*' or '/'
 *     <number2>        another arbitrary decimal number
 * Any white spaces can be inserted between two elements.
 *
 * input:
 *     input            input string which contains a formula (IN)
 *     output           output buffer for storing a result (OUT)
 * return:              error code
 *
 */
EXPORT ER tet_calc(UB *input, UB *output)
{
  ER ercd;

  if (input == NULL || output == NULL) {
    return E_PAR;
  }

  /* calculation procedure */
  {
    UB *p, *q;
    INT num1, num2, result;
    CalcOp op;

    ercd = E_OK;
    p = input;

    /* skip white spaces */
    while (*p == ' ') { p++; }
    /* parse the first digits */
    num1 = 0;
    q = p;
    while (*q >= '0' && *q <= '9') {
      num1 = (num1 * 10) + (*q - '0');
      q++;
    }
    if (p == q) {
      /* parse error */
      ercd = E_OBJ;
      goto EXIT;
    }
    p = q;
    /* skip white spaces */
    while (*p == ' ') { p++; }
    /* parse an operand. error if other character is found. */
    switch (*p++) {
    case '+':
      op = OP_PLUS;
      break;
    case '-':
      op = OP_MINUS;
      break;
    case '*':
      op = OP_MUL;
      break;
    case '/':
      op = OP_DIV;
      break;
    default:
      /* parse error */
      ercd = E_OBJ;
      goto EXIT;
      /*NOTREACHED*/
      break;
    }
    /* skip white spaces */
    while (*p == ' ') { p++; }
    /* parse the second digits */
    num2 = 0;
    q = p;
    while (*q >= '0' && *q <= '9') {
      num2 = (num2 * 10) + (*q - '0');
      q++;
    }
    if (p == q) {
      /* parse error */
      ercd = E_OBJ;
      goto EXIT;
    }
    p = q;
    /* skip white spaces */
    while (*p == ' ') { p++; }
    /* check if a null character is found */
    if (*p != '\0') {
      /* parse error */
      ercd = E_OBJ;
      goto EXIT;
    }

    if (ercd == E_OK) {
      /* calculate the parsed formula */
      result = 0;
      switch (op) {
      case OP_PLUS:
        result = num1 + num2;
        break;
      case OP_MINUS:
        result = num1 - num2;
        break;
      case OP_MUL:
        result = num1 * num2;
        break;
      case OP_DIV:
        result = num1 / num2;
        break;
      default:
        ercd = E_OBJ;
        goto EXIT;
        /*NOTREACHED*/
        break;
      }
    }
    /* set the result to output buffer */
    sprintf(output, "%d\n", result);
  }

EXIT:
  return ercd;
}