Peter's_Calculator.cpp

#include <stdio.h>
#include <stack>
#include <string.h>
#include <algorithm>
#include <ctype.h>
#include <iostream>
#include <sstream>
#include <map>
using namespace std;
int priority_op(char c) {
    switch(c) {
        case '(':return 0;
        case '+': case '-':return 1;
        case '*': case '/':return 2;
    }
    return -1;
}
int isoperator(char c) {
    switch(c) {
        case '(':case ')':case '+': case '-':case '*': case '/':return 1;
    }
    return 0;
}
int isvariable(string token) {
 return isalpha(token[0]);
}
void trans(const char *infix, char buffer[]) {
    int len = strlen(infix), prevOp = 1;
    char *ptr = buffer;
    stack<char> op;
    *ptr = '\0';
    for(int i = 0; i < len; i++) {
        if(isalpha(infix[i]) || isdigit(infix[i]) 
   || (infix[i] == '-' && isdigit(infix[i+1]) && prevOp)) {
   prevOp = 0;
         sprintf(ptr, "%c", infix[i]), i++;
         while(*ptr)    ptr++;
   while(isalpha(infix[i]) || isdigit(infix[i])) {
             sprintf(ptr, "%c", infix[i]), i++;
             while(*ptr)    ptr++;
            }
            sprintf(ptr, " "), i--;
            while(*ptr)  ptr++;
        } else {
         prevOp = 0;
            if(infix[i] == ')') {
                while(!op.empty() && op.top() != '(') {
                    sprintf(ptr, "%c ", op.top()), op.pop();
                    while(*ptr) ptr++;
                }
                op.pop();
            } else {
                if(infix[i] != '(') {
                 while(!op.empty() && priority_op(op.top()) >= priority_op(infix[i])) {
                     sprintf(ptr, "%c ", op.top()), op.pop();
                     while(*ptr) ptr++;
                 }
             }
          prevOp = 1;
                op.push(infix[i]);
            }
        }
    }
    while(!op.empty()) {
        sprintf(ptr, "%c ", op.top()), op.pop();
        while(*ptr) ptr++;
    }
}
void trimWhiteSpace(char s[]) {
 int j = 0;
 for(int i = 0; s[i]; i++)
  if(!isspace(s[i]))
   s[j++] = s[i];
 s[j] = '\0';
}
map<string, string> VAL_exp;
map<string, int> VAL_val;
map<string, int> VAL_stk;
int error_FLAG;
int calcPostfix(const char* postfix);
int getValue(string VAL_name) {
    if(!isvariable(VAL_name)) {
     stringstream scin(VAL_name);
     int value;
     scin >> value;
     return value;
    }
 if(VAL_exp.find(VAL_name) == VAL_exp.end() || VAL_stk[VAL_name]) {
  error_FLAG = 1;
  return 0;
 }
 if(VAL_val.find(VAL_name) == VAL_val.end()) {
  VAL_stk[VAL_name] = 1;
//  cout << "solving " << VAL_name << ", " << VAL_exp[VAL_name] << endl; 
  VAL_val[VAL_name] = calcPostfix(VAL_exp[VAL_name].c_str());
//  cout << "solved " << VAL_name << ", val = " << VAL_val[VAL_name] << endl;
  VAL_stk[VAL_name] = 0;
 }
 return VAL_val[VAL_name];
}
int calcPostfix(const char* postfix) {
 stringstream  scin(postfix);
    stack<int>   stk;
 string   token;
    int    a, b;
    
    while(scin >> token) {
     if(token.length() == 1 && isoperator(token[0])) {
            b = stk.top(), stk.pop();
            a = stk.top(), stk.pop();
            switch(token[0]) {
                case '+': a = a+b;break;
                case '-': a = a-b;break;
                case '*': a = a*b;break;
                case '/': a = a/b;break;
            }
            stk.push(a);
     } else {
      stk.push(getValue(token));
     }
     if(error_FLAG) return 0;
    }
    return stk.top();
}
void printVal(string valName) {
 error_FLAG = 0;
 VAL_val.clear();
 VAL_stk.clear();
 int val = getValue(valName);
 if(error_FLAG)
  puts("UNDEF");
 else
  printf("%d\n", val);
}
int main() {
// freopen("input.txt", "r+t", stdin);
// freopen("out.txt", "w+t", stdout); 
 string  LHS, RHS;
 int  pos;
 char  postfix[32767], lines[32767];
 
    while(gets(lines)) {
     trimWhiteSpace(lines);
     string str(lines);
     if(str.find(":=") != string::npos) {
      pos = str.find(":=");
      LHS = str.substr(0, pos);
      RHS = str.substr(pos + 2);
      trans(RHS.c_str(), postfix);
      VAL_exp[LHS] = postfix;
     } else if(str.find("PRINT") != string::npos) {
      pos = str.find("PRINT");
      RHS = str.substr(pos + 5);
      printVal(RHS);
     } else if(str.find("RESET") != string::npos) {
      VAL_exp.clear();
     }
    }
    return 0;
}