AOJ 0109 Smart Calculator

Smart Calculator

Your task is to write a program which reads an expression and evaluates it.

The expression consists of numerical values, operators and parentheses, and the ends with '='.
The operators includes +, - , *, / where respectively represents, addition, subtraction, multiplication and division.
Precedence of the operators is based on usual laws. That is one should perform all multiplication and division first, then addition and subtraction. When two operators have the same precedence, they are applied from left to right.
You may assume that there is no division by zero.
All calculation is performed as integers, and after the decimal point should be truncated
Length of the expression will not exceed 100.
Input

The input is a sequence of datasets. The first line contains an integer n which represents the number of datasets. There will be n lines where each line contains an expression.

Output

For each datasets, prints the result of calculation.

Sample Input

2
4-2*3=
4*(8+4+3)=
Output for the Sample Input

-2
60

#include <string>
#include <cctype>
#include<iostream>
#include<map>
#include<sstream>
using namespace std;
istream* input;
int no_of_errors;
enum Token_value {
  END,NUMBER,PLUS='+',MINUS='-',MUL='*',DIV='/',
  PRINT=';',ASSIGN='=',LP='(',RP=')'
};
Token_value curr_tok = PRINT;
int number_value;
string string_value;
Token_value get_token()
{
  char ch;
  do {
    if(!input->get(ch)) return curr_tok = END;
  } while (ch!='\n' && isspace(ch));
 
  switch (ch) {
  case ';':
  case '\n':
    return curr_tok=PRINT;
  case '*':
  case '/':
  case '+':
  case '-':
  case '(':
  case ')':
  case '=':
return curr_tok=Token_value(ch);
  case '0': case '1': case '2': case '3': case '4':
case '5': case '6': case '7': case '8': case '9':
    input->putback(ch);
    *input >> number_value;
    return curr_tok=NUMBER;
  }
}
int expr(bool);
int prim(bool get)
{
  if (get) get_token();
  switch (curr_tok) {
  case NUMBER:
    { int v = number_value;
      get_token();
      return v;
    }
  case MINUS:
    return -prim(true);
  case LP:
    { int e = expr(true);
      get_token();
      return e;
    }
  }
}
int term(bool get)
{
  int left = prim(get);
  for (;;)
    switch (curr_tok) {
    case MUL:
      left *= prim(true);
      break;
    case DIV:
      if (int d = prim(true)) {
left /= d;
break;
      }
    default:
      return left;
    }
}
int expr(bool get)
{
  int left = term(get);
  for (;;)
    switch (curr_tok) {
    case PLUS:
      left += term(true);
      break;
    case MINUS:
      left -= term(true);
      break;
    default:
      return left;
    }
}
int main()
{
  int n;
  input = &cin;
  cin>>n;
  while(n--){
    while (*input) {
      get_token();
      if (curr_tok == END) break;
      if (curr_tok == PRINT) continue;
      cout << expr(false) << '\n';
    }
  }
  return no_of_errors;
}