给出错误答案的表达式树
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这是家庭作业,因此请不要直接使用代码。只是提示,谢谢!
我正在开发一个项目,该项目将使用表达式树来派生各种事物,然后对它们执行操作。现在我不太担心推导部分,我只想把操作部分搞下来。
我使用的表达式树代码适用于整数,但是一旦我输入“x”或任何其他变量,我的答案就是错误的。我的程序使用后缀表达式字符串...下面是正确和错误的示例。
5 6 + 返回 11。正确
5x 6x + 返回 11。不正确需要是 11x
这是我的代码:
// This is the expression tree code I'm using
#ifndef EXPRNODE_H
#define EXPRNODE_H
#include <cstdlib> // for NULL
using namespace std;
//====================================== class ExprNode
class ExprNode {
public:
ExprNode(char oper, ExprNode* left, ExprNode* right);
ExprNode(int val);
int eval() const; // Evaluate expr tree. Return result.
private:
char _op; // one of +, -, *, /, #
int _value; // integer value used for constants.
ExprNode* _left; // left subtree
ExprNode* _right; // right subtree
};
#endif
//============================================= ExprNode constructor
// Constructs node for a binary operator.
ExprNode::ExprNode(char oper, ExprNode* left, ExprNode* right) {
_op = oper;
_left = left;
_right = right;
}
//============================================== ExprNode constructor
// Constructs a node for an integer constant
ExprNode::ExprNode(int v) {
_op = '#';
_value = v;
_left = NULL;
_right = NULL;
}
//===================================================== ExprNode::eval
int ExprNode::eval() const {
// Recursively evaluate expression tree and return result.
int result;
switch (_op) {
case '+':
result = _left->eval() + _right->eval();
break;
case '-':
result = _left->eval() - _right->eval();
break;
case '*':
result = _left->eval() * _right->eval();
break;
case '/':
result = _left->eval() / _right->eval();
break;
case '#':
result = _value; // an integer constant
break;
}
return result;
}
bool isOperator (char operand)
{
return operand == '+' || operand == '-' || operand == '*' || operand == '/' || operand == '^';
}
bool isNumber (char potentialNumber)
{
return potentialNumber >= '0' && potentialNumber <= '9';
}
bool isX (char letter)
{
return letter == 'x' || letter == 'X';
}
我不会包含从中缀到后缀的代码,因为它是不必要的(我认为).... 接下来是表达式树和计算的代码
// the expression string is the postfix expression I returned previously
void expressionTree(string expression)
{
string tempNum = "";
string tempNum2 = "";
int count = 1;
int tempNumInt;
int tempNum2Int;
// creates a blank total value and blank numbers
ExprNode* totalVal = new ExprNode('+', new ExprNode(0), new ExprNode(0));
ExprNode* tNum;
ExprNode* tNum2;
// loop through the postfix expression
for (unsigned int iterator = 0; iterator < expression.length(); iterator++)
{
if (isOperator(expression[iterator]))
{
// Don't need to worry about at the moment
if (expression[iterator] == '^')
{
// go to derivative later
}
else
{
if (count % 2 != 0)
{
// we'll do different derivatives here.... for now just add, subtract, multiply, divide
totalVal = new ExprNode(expression[iterator], tNum, tNum2);
}
else if (count % 2 == 0 && expression[iterator] == '+' || expression[iterator] == '*')
{
totalVal = new ExprNode(expression[iterator], tNum, totalVal);
}
else if (count % 2 == 0 && expression[iterator] == '-' || expression[iterator] == '/')
{
totalVal = new ExprNode(expression[iterator], totalVal, tNum);
}
}
count++;
}
if (isNumber(expression[iterator]) && count % 2 != 0)
{
tempNum += expression[iterator];
}
else if (isNumber(expression[iterator]) && count % 2 == 0)
{
tempNum2 += expression[iterator];
}
if (expression[iterator] == ' ' && count % 2 != 0)
{
tempNumInt = atoi (tempNum.c_str());
tNum = new ExprNode(tempNumInt);
tempNum = "";
count++;
}
else if (expression[iterator] == ' ' && count % 2 == 0)
{
tempNum2Int = atoi (tempNum2.c_str());
tNum2 = new ExprNode(tempNum2Int);
tempNum2 = "";
count++;
}
else if (expression[iterator] == ' ')
{
count++;
}
}
cout << totalVal->eval() << endl;
}
我将尝试解释任何不清楚的内容。提前致谢。
EDIT
This is homework so no straight up code please. Just hints, thank you!
I'm working on a project that will use an expression tree to derive a variety of things and then perform operations on them. Right now I'm not too worried about the deriving part, I just want to get the operations part down.
The expression tree code that I'm using works for integers but once I input "x" or any other variable my answer is wrong. My program works with postfix expression strings... below is an example of what is right and wrong.
5 6 + returns 11. correct
5x 6x + returns 11. incorrect needs to be 11x
Here is my code:
// This is the expression tree code I'm using
#ifndef EXPRNODE_H
#define EXPRNODE_H
#include <cstdlib> // for NULL
using namespace std;
//====================================== class ExprNode
class ExprNode {
public:
ExprNode(char oper, ExprNode* left, ExprNode* right);
ExprNode(int val);
int eval() const; // Evaluate expr tree. Return result.
private:
char _op; // one of +, -, *, /, #
int _value; // integer value used for constants.
ExprNode* _left; // left subtree
ExprNode* _right; // right subtree
};
#endif
//============================================= ExprNode constructor
// Constructs node for a binary operator.
ExprNode::ExprNode(char oper, ExprNode* left, ExprNode* right) {
_op = oper;
_left = left;
_right = right;
}
//============================================== ExprNode constructor
// Constructs a node for an integer constant
ExprNode::ExprNode(int v) {
_op = '#';
_value = v;
_left = NULL;
_right = NULL;
}
//===================================================== ExprNode::eval
int ExprNode::eval() const {
// Recursively evaluate expression tree and return result.
int result;
switch (_op) {
case '+':
result = _left->eval() + _right->eval();
break;
case '-':
result = _left->eval() - _right->eval();
break;
case '*':
result = _left->eval() * _right->eval();
break;
case '/':
result = _left->eval() / _right->eval();
break;
case '#':
result = _value; // an integer constant
break;
}
return result;
}
bool isOperator (char operand)
{
return operand == '+' || operand == '-' || operand == '*' || operand == '/' || operand == '^';
}
bool isNumber (char potentialNumber)
{
return potentialNumber >= '0' && potentialNumber <= '9';
}
bool isX (char letter)
{
return letter == 'x' || letter == 'X';
}
I'm not going to include the code going from infix to postfix because it is unnecessary (I think).... next is the code for the expression tree and calculations
// the expression string is the postfix expression I returned previously
void expressionTree(string expression)
{
string tempNum = "";
string tempNum2 = "";
int count = 1;
int tempNumInt;
int tempNum2Int;
// creates a blank total value and blank numbers
ExprNode* totalVal = new ExprNode('+', new ExprNode(0), new ExprNode(0));
ExprNode* tNum;
ExprNode* tNum2;
// loop through the postfix expression
for (unsigned int iterator = 0; iterator < expression.length(); iterator++)
{
if (isOperator(expression[iterator]))
{
// Don't need to worry about at the moment
if (expression[iterator] == '^')
{
// go to derivative later
}
else
{
if (count % 2 != 0)
{
// we'll do different derivatives here.... for now just add, subtract, multiply, divide
totalVal = new ExprNode(expression[iterator], tNum, tNum2);
}
else if (count % 2 == 0 && expression[iterator] == '+' || expression[iterator] == '*')
{
totalVal = new ExprNode(expression[iterator], tNum, totalVal);
}
else if (count % 2 == 0 && expression[iterator] == '-' || expression[iterator] == '/')
{
totalVal = new ExprNode(expression[iterator], totalVal, tNum);
}
}
count++;
}
if (isNumber(expression[iterator]) && count % 2 != 0)
{
tempNum += expression[iterator];
}
else if (isNumber(expression[iterator]) && count % 2 == 0)
{
tempNum2 += expression[iterator];
}
if (expression[iterator] == ' ' && count % 2 != 0)
{
tempNumInt = atoi (tempNum.c_str());
tNum = new ExprNode(tempNumInt);
tempNum = "";
count++;
}
else if (expression[iterator] == ' ' && count % 2 == 0)
{
tempNum2Int = atoi (tempNum2.c_str());
tNum2 = new ExprNode(tempNum2Int);
tempNum2 = "";
count++;
}
else if (expression[iterator] == ' ')
{
count++;
}
}
cout << totalVal->eval() << endl;
}
I'll try to explain anything that is unclear. Thanks in advance.
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我并不是指出确切的错误,而是给你一个建议:int ExprNode::eval() const 不应该返回 'int'。这不足以处理变量结果,例如“11x”(这不能用简单的 int 表示)。您必须创建自己的结构来存储结果的整数部分和变量部分(最后一个是可选的)。
I'm not pointing out the exact mistake, but giving you an advice: int ExprNode::eval() const should not return 'int'. That's not enough to handle the variable results, like "11x" (this cannot be represented with a simple int). You'll have to create your own structure that stores the integer part and the variable part of the result (with this last one being optional).