Data Structures using C++

 Program Limitations 
  * This program Only process single digit operations 
  * Can't handle unary operation 
  * Only process left to right associativity
  #include< iostream > 
  #include< cmath > 
  #include< cstdlib > 
  #include< string > 
  #define MAX_SIZE 20 
  using namespace std; 
  template< class T > 
  class Stack 
  { 
     private: 
        T item[MAX_SIZE]; 
        int top; 
     public: 
        Stack() 
        { 
          top = -1; 
        } 
      void push(T data) 
      { 
         if(!this->is_full()) 
            item[++top] = data; 
         else 
         { 
            cout<<"Stack Error"<< endl; 
            exit(10); 
         } 
      } 
      T pop() 
      { 
         if(!this->is_empty()) 
            return item[top--]; 
         else 
         { 
            cout<<"Stack is Empty"<< endl; 
            exit(11); 
         } 
      } 
      int size() 
      { 
         return top+1; 
      } 
      bool is_empty() 
      { 
         if(top==-1) 
            return true; 
         else 
            return false; 
      } 
      bool is_full() 
      { 
         if(top==MAX_SIZE-1) 
            return true; 
         else 
            return false; 
      } 
      void display() 
      { 
         for(int i=0; i< this->size(); i++) 
         { 
            cout<< item[i]<<" "; 
         } 
         cout<< endl; 
      } 
      T return_top() 
      { 
         return item[top]; 
      } 
  }; 
  class Convert 
  { 
      private: 
        bool num_flag; 
        bool two_digit_flag; 
      public: 
        Convert(); 
        string return_with_bracket(string infix); 
        void to_Postfix(string infix,char postfix[]); 
        bool prcd(char op1, char op2); 
        int isOperand(char op); 
        int isOperator(char op); 
        bool return_flag() 
        { 
          return num_flag; 
        } 
  }; 
  Convert::Convert() 
  { 
     this->num_flag = false; 
     this->two_digit_flag = false; 
  } 
  string Convert::return_with_bracket(string infix) 
  { 
     return("(" + infix + ")"); 
  } 
  bool Convert::prcd(char op1, char op2) 
  { 
      if((op1=='+' || op1=='-' || op1=='*' || op1=='/') && op2=='(' ) 
        return true; 
      if(op1=='+' && op2=='+') 
        return true; 
      if(op1=='-' && op2=='-') 
        return false; 
      if(op1=='-' && op2=='+') 
        return false; 
      if(op1=='+' && op2=='-') 
        return false; 
      if(op1=='/' && op2=='/') 
        return false; 
      if(op1=='/' && (op2=='-' || op2=='+')) 
        return true; 
      if(op1=='*' && (op2=='+' || op2=='-')) 
        return true; 
      if((op1 == '-' || op1 == '+') && (op2 =='*' || op2 == '/')) 
        return false; 
      if((op1 == '$' || op1 == '+') && (op2 =='*' || op2 == '/' || op2=='-')) 
        return true; 
      if((op1 == '-' || op1 == '+' || op1 =='*' || op1 == '/')&& op2=='^') 
        return false; 
      if(op1 == '^' && ( op2 == '+' || op2 =='*' || op2 == '/' || op2=='-')) 
        return false; 
  } 
  int Convert::isOperand(char op) 
  { 
     return(op>= '0' && op <= '9'); 
  } 
  int Convert::isOperator(char op) 
  { 
     return(op=='+' || op=='-' || op == '/' || op=='*' || op=='^'); 
  } 
  void Convert::to_Postfix(string infix, char postfix[]) 
  { 
     int position, outpos=0; 
     char c; 
     int count = 0; 
     char temp; 
     char stacktop ; 
     Stack < char > stack; 
     for(position = 0; (c = infix[position])!='\0'; position++) 
     { 
        if(this->isOperand(c)) 
        { 
          postfix[outpos++] = c; 
          this->num_flag = true; 
          count++; 
          if(count>=2) 
          { 
            this->two_digit_flag = true; 
          } 
        } 
        else if(this->isOperator(c)) 
        { 
          count = 0; 
          if(isOperator(infix[position]) && isOperator(infix[position+1])) 
          { 
            cout<<"\aMissing argument in between "<< infix[position]<<" and "<< infix[position+1] 
            <<" in column "<< position+1<< endl; 
            exit(9); 
          } 
          if(this->prcd(c, stacktop)) 
          { 
            stacktop=stack.return_top(); 
            stack.push(c); 
            stacktop = c; 
          } 
          else 
          { 
            while(true) 
            { 
              temp = stack.pop(); 
              postfix[outpos++] =temp; 
              stacktop = stack.return_top(); 
              if(prcd(c, stacktop) || stacktop=='(') 
              break; 
            } 
            stack.push(c); 
            stacktop = stack.return_top(); 
          } 
        } 
        else if(c=='(') 
        { 
          count = 0; 
          stack.push(c); 
          stacktop = stack.return_top(); 
        } 
        else if(c==')') 
        { 
          count = 0; 
          while(1) 
          { 
            if(stack.size()==0) 
            { 
              cout<<"Warning!! Number of ')' is greater than '('" << endl; 
              exit(2); 
            } 
            temp = stack.pop(); 
            if(temp!='(') 
            { 
              postfix[outpos++] = temp; 
            } 
            else 
            { 
              break; 
            } 
          } 
          stacktop =stack.return_top(); 
        } 
        else 
        { 
          cout<<"Invalid input"; 
          exit(3); 
        } 
        if(infix[position]==')' && infix[position+1]=='(') 
        { 
          stack.push('*'); 
          stacktop = stack.return_top(); 
        } 
    } 
        if(stack.size()!=0) 
        { 
        cout<<"Warning!!Number of '(' is greater than ')'"<< endl; 
        // exit(6); 
        } 
        if(!this->return_flag()) 
        { 
        cout<<"You must Enter Numeric value for calculation"<< endl; 
        cout<<"This program cannot perform operations on variables"; 
        exit(5); 
        } 
        if(this->two_digit_flag) 
        { 
        cout<<"Sory! Althoug u may have entered right string"<< endl; 
        cout<<"this program is only for single digit operation"<< endl; 
        exit(8); 
        } 
        postfix[outpos] = '\0'; 
  } 
  class Evaluate 
  { 
     public: 
       double eval(char expr[], Convert &); 
       double oper(int symb, double op1, double op2); 
  }; 
  double Evaluate::oper(int symb, double op1, double op2) 
  { 
     switch(symb) 
     { 
        case '+': return (op1 + op2); 
        case '-': return (op1 - op2); 
        case '*': return (op1 * op2); 
        case '/': return (op1 / op2); 
        case '^': return (pow(op1, op2)); 
     } 
  } 
  double Evaluate::eval(char expr[],Convert &convert) 
  { 
      int c, position; 
      char temp1; 
      int count = 0; 
      double opnd1, opnd2, value; 
      Stack< double > stack; 
      for(position = 0; (c = expr[position])!='\0'; position++) 
      { 
        if(convert.isOperand(c)) 
        { 
          temp1 = double(c-'0'); 
          stack.push(temp1); 
        } 
        else 
        { 
          opnd2 = stack.pop(); 
          if(stack.size()==0) 
          { 
            cout<<"This program cannot process unary operation"; 
            exit(1); 
          } 
          opnd1 = stack.pop(); 
          value = oper(c, opnd1, opnd2); 
          stack.push(value); 
        } 
      } 
      if(stack.size()>=2) 
      { 
        cout<<"Sory! this program cannot calculate this"<< endl; 
        cout<<"Enter +, *, /, - or ^ between bracket"<< endl; 
        exit(4); 
      } 
      return (stack.pop()); 
  } 
  int main() 
  { 
      Convert convert; 
      Evaluate evaluate; 
      string bracketted_infix; 
      char infix[50], postfix[50]; 
      char choice; 
      while(1) 
      { 
        cout<<"Enter string: "; 
        cin>>infix; 
        cout<< endl; 
        cout<<"Entered String: "<< infix<< endl; 
        bracketted_infix = convert.return_with_bracket(infix); 
        convert.to_Postfix(bracketted_infix, postfix); 
        cout<<"Equivalent Postfix string: "<< postfix<< endl; 
        cout<<"RESULT: "; 
        cout<< evaluate.eval(postfix, convert); 
        cout<<"\nCalculate another string?(y/n) "; 
        cin>>choice; 
        cout<< endl; 
        if(choice=='n') 
          break; 
      } 
      return 0; 
  }