我的讲师给了我一个分配来创建一个程序来转换和使用Stacks将表达式中缀到postfix。我已经制作了堆栈类和一些函数来读取中缀表达式。
但是这个名为convertToPostfix(char * const inFix, char * const postFix)的函数负责将数组inFix中的inFix表达式转换为使用堆栈的postFix数组中的post fix表达式，但这并不是它想要做的。你能帮助我，告诉我我做错了吗？
以下是从inFix转换为postFix的函数的代码，convertToPostfix(char * const inFix, char * const postFix)是我需要帮助修复的代码：
void ArithmeticExpression::inputAndConvertToPostfix()
{
char inputChar; //declaring inputChar
int i = 0; //inizalize i to 0
cout << "Enter the Arithmetic Expression(No Spaces): ";
while( ( inputChar = static_cast<char>( cin.get() ) ) != '\n' )
{
if (i >= MAXSIZE) break; //exits program if i is greater than or equal to 100
if(isdigit(inputChar) || isOperator(inputChar))
{
inFix[i] = inputChar; //copies each char to inFix array
cout << inFix[i] << endl;
}
else
cout << "You entered an invalid Arithmetic Expression\n\n" ;
}
// increment i;
i++;
convertToPostfix(inFix, postFix);
}
bool ArithmeticExpression::isOperator(char currentChar)
{
if(currentChar == '+')
return true;
else if(currentChar == '-')
return true;
else if(currentChar == '*')
return true;
else if(currentChar == '/')
return true;
else if(currentChar == '^')
return true;
else if(currentChar == '%')
return true;
else
return false;
}
bool ArithmeticExpression::precedence(char operator1, char operator2)
{
if ( operator1 == '^' )
return true;
else if ( operator2 == '^' )
return false;
else if ( operator1 == '*' || operator1 == '/' )
return true;
else if ( operator1 == '+' || operator1 == '-' )
if ( operator2 == '*' || operator2 == '/' )
return false;
else
return true;
return false;
}
void ArithmeticExpression::convertToPostfix(char * const inFix, char * const postFix)
{
Stack2<char> stack;
const char lp = '(';
stack.push(lp); //Push a left parenthesis ‘(‘ onto the stack.
strcat(inFix,")");//Appends a right parenthesis ‘)’ to the end of infix.
// int i = 0;
int j = 0;
if(!stack.isEmpty())
{
for(int i = 0;i < 100;){
if(isdigit(inFix[i]))
{
postFix[j] = inFix[i];
cout << "This is Post Fix for the first If: " << postFix[j] << endl;
i++;
j++;
}
if(inFix[i] == '(')
{
stack.push(inFix[i]);
cout << "The InFix was a (" << endl;
i++;
//j++;
}
if(isOperator(inFix[i]))
{
char operator1 = inFix[i];
cout << "CUrrent inFix is a operator" << endl;
if(isOperator(stack.getTopPtr()->getData()))
{
cout << "The stack top ptr is a operator1" << endl;
char operator2 = stack.getTopPtr()->getData();
if(precedence(operator1,operator2))
{
//if(isOperator(stack.getTopPtr()->getData())){
cout << "The stack top ptr is a operato2" << endl;
postFix[j] = stack.pop();
cout << "this is post fix " << postFix[j] << endl;
i++;
j++;
// }
}
}
else
stack.push(inFix[i]);
// cout << "Top Ptr is a: "<< stack.getTopPtr()->getData() << endl;
}
for(int r = 0;r != '\0';r++)
cout << postFix[r] << " ";
if(inFix[i] == ')')
{
while(stack.stackTop()!= '(')
{
postFix[j] = stack.pop();
i++;
j++;
}
stack.pop();
}
}
}
}
注意使用此算法生成convertToPostfix函数：
当堆栈不为空时，从左到右读取中缀并执行以下操作：
如果中缀中的当前字符是运算符，
答案 0 :(得分：7)
这基本上是对Yuushi答案的评论。
precedence(rightOp, leftOp)）。然后你应该记录结果意味着什么 - 现在你返回true如果a rOp b lOp c == (a rOp b) lOp c（是的，运营商订单与你所说的不匹配 - “+”和“ - ”在两个订单中都不相同，例如）。a - b * c后，输出为a b c且堆栈为[- *]。现在你读了一个+，你需要弹出两个运算符，结果是a b c * -。即，输入a - b * c + d应该导致a b c * - d + 更新：附加完整解决方案（根据Yuushi的回答）：
bool isOperator(char currentChar)
{
switch (currentChar) {
case '+':
case '-':
case '*':
case '/':
case '^':
case '%':
return true;
default:
return false;
}
}
// returns whether a `lOp` b `rOp` c == (a `lOp` b) `rOp` c
bool precedence(char leftOperator, char rightOperator)
{
if ( leftOperator == '^' ) {
return true;
} else if ( rightOperator == '^' ) {
return false;
} else if ( leftOperator == '*' || leftOperator == '/' || leftOperator == '%' ) {
return true;
} else if ( rightOperator == '*' || rightOperator == '/' || rightOperator == '%' ) {
return false;
}
return true;
}
#include <stdexcept>
#include <cctype>
#include <sstream>
#include <stack>
std::string convertToPostfix(const std::string& infix)
{
std::stringstream postfix; // Our return string
std::stack<char> stack;
stack.push('('); // Push a left parenthesis ‘(‘ onto the stack.
for(std::size_t i = 0, l = infix.size(); i < l; ++i) {
const char current = infix[i];
if (isspace(current)) {
// ignore
}
// If it's a digit or '.' or a letter ("variables"), add it to the output
else if(isalnum(current) || '.' == current) {
postfix << current;
}
else if('(' == current) {
stack.push(current);
}
else if(isOperator(current)) {
char rightOperator = current;
while(!stack.empty() && isOperator(stack.top()) && precedence(stack.top(), rightOperator)) {
postfix << ' ' << stack.top();
stack.pop();
}
postfix << ' ';
stack.push(rightOperator);
}
// We've hit a right parens
else if(')' == current) {
// While top of stack is not a left parens
while(!stack.empty() && '(' != stack.top()) {
postfix << ' ' << stack.top();
stack.pop();
}
if (stack.empty()) {
throw std::runtime_error("missing left paren");
}
// Discard the left paren
stack.pop();
postfix << ' ';
} else {
throw std::runtime_error("invalid input character");
}
}
// Started with a left paren, now close it:
// While top of stack is not a left paren
while(!stack.empty() && '(' != stack.top()) {
postfix << ' ' << stack.top();
stack.pop();
}
if (stack.empty()) {
throw std::runtime_error("missing left paren");
}
// Discard the left paren
stack.pop();
// all open parens should be closed now -> empty stack
if (!stack.empty()) {
throw std::runtime_error("missing right paren");
}
return postfix.str();
}
#include <iostream>
#include <string>
int main()
{
for (;;) {
if (!std::cout.good()) break;
std::cout << "Enter the Arithmetic Expression: ";
std::string infix;
std::getline(std::cin, infix);
if (infix.empty()) break;
std::cout << "Postfix: '" << convertToPostfix(infix) << "'\n";
}
return 0;
}
答案 1 :(得分：2)
因此您的代码存在许多问题。我会发布一些（应该是）一个更正的解决方案，它有大量的评论来解释发生了什么以及你犯了哪些错误。前面的一些事情：
我会使用std::string代替char *，因为它会让事情变得更清晰，老实说，你应该在C++中使用它，除非你有充分的理由不要（例如与C库的互操作性）。此版本还会返回string，而不是将char *作为参数。
我正在使用标准库<stack>中的堆栈，这与您的家庭堆栈略有不同。 top()向您显示下一个元素，不用将其从堆栈中删除，pop()返回void，但从堆栈中删除顶部元素。
这是一个免费的功能，不是课程的一部分，但应该很容易修改 - 这对我来说更容易进行测试。
我不相信你的运营商优先权表是正确的，但是，我会让你仔细检查一下。
#include <stack>
#include <cctype>
#include <iostream>
std::string convertToPostfix(std::string& infix)
{
std::string postfix; //Our return string
std::stack<char> stack;
stack.push('('); //Push a left parenthesis ‘(‘ onto the stack.
infix.push_back(')');
//We know we need to process every element in the string,
//so let's do that instead of having to worry about
//hardcoded numbers and i, j indecies
for(std::size_t i = 0; i < infix.size(); ++i) {
//If it's a digit, add it to the output
//Also, if it's a space, add it to the output
//this makes it look a bit nicer
if(isdigit(infix[i]) || isspace(infix[i])) {
postfix.push_back(infix[i]);
}
//Already iterating over i, so
//don't need to worry about i++
//Also, these options are all mutually exclusive,
//so they should be else if instead of if.
//(Mutually exclusive in that if something is a digit,
//it can't be a parens or an operator or anything else).
else if(infix[i] == '(') {
stack.push(infix[i]);
}
//This is farily similar to your code, but cleaned up.
//With strings we can simply push_back instead of having
//to worry about incrementing some counter.
else if(isOperator(infix[i]))
{
char operator1 = infix[i];
if(isOperator(stack.top())) {
while(!stack.empty() && precedence(operator1,stack.top())) {
postfix.push_back(stack.top());
stack.pop();
}
}
//This shouldn't be in an else - we always want to push the
//operator onto the stack
stack.push(operator1);
}
//We've hit a right parens - Why you had a for loop
//here originally I don't know
else if(infix[i] == ')') {
//While top of stack is not a right parens
while(stack.top() != '(') {
//Insert into postfix and pop the stack
postfix.push_back(stack.top());
stack.pop();
}
// Discard the left parens - you'd forgotten to do this
stack.pop();
}
}
//Remove any remaining operators from the stack
while(!stack.empty()) {
postfix.push_back(stack.top());
stack.pop();
}
}
答案 2 :(得分：0)
这是我的C使用多位数评估。
#include <stdio.h>
#include <math.h>
#define MAX 50
void push(char[],char);
void in_push(double[], double);
int pop();
int prec(char);
double eval(char[],int,double[]);
int top = 0;
void main() {
double eval_stack[MAX];
int op_count=0;
char stack[MAX], exps[MAX], symbols[MAX];
int i=0,j=0,len,check;
while((symbols[i]=getchar())!='\n') {
if(symbols[i]!=' ' || symbols[i]!='\t') {
if(symbols[i]=='+' || symbols[i]=='-' || symbols[i]=='/' || symbols[i]=='*' || symbols[i]=='^')
op_count++;
i++;
}
}
symbols[i]='#';
symbols[++i]='\0';
len = strlen(symbols);
stack[top] = '#';
for(i=0; i<=len; i++) {
if(symbols[i]>='a' && symbols[i]<='z') {
exps[j]=symbols[i];
j++;
}
switch(symbols[i]) {
case '0': case '1': case '2': case '3': case '4': case '5': case '6': case '7': case '8': case '9':
//if(symbols[i]>='a' && symbols[i]<='z') {
exps[j]=symbols[i];
j++;
break;
case '+': case '-': case '*': case '/': case '^':
exps[j++] = ' ';
while(prec(symbols[i]) <= prec(stack[top])) {
exps[j] = stack[top];
pop();
//printf("\n\t\t%d\t\t%d\n", top,j);
j++;
}
if(prec(symbols[i]) > prec(stack[top])) {
push(stack,symbols[i]);
}
break;
case '(':
push(stack,symbols[i]);
break;
case ')':
while(stack[top]!='(') {
exps[j] = stack[top];
pop();
j++;
}
pop();
break;
case '#':
exps[j++] = ' ';
while(stack[top]!='#') {
exps[j] = stack[top];
pop();
j++;
}
pop();
break;
}
}
exps[j]='\0';
printf("Postfix: %s", exps);
for(i=0; i<j; i++)
if(exps[i]=='a')
check = 1;
if(check!=1)
printf("\nSolution: %.1f", eval(exps,j,eval_stack));
}
double eval(char exps[],int exps_len,double eval_stack[]) {
int i; int len=exps_len,temp;
double in_temp[MAX],t;
int count,power,j,in_count;
count=power=j=t=in_count=0;
double result;
for(i=0; i<len; i++) {
switch(exps[i]) {
case '0': case '1': case '2': case '3': case '4': case '5': case '6': case '7': case '8': case '9':
in_temp[i] = exps[i]-'0';
j=i+1;
while(exps[j]>='0' && exps[j]<='9') {
in_temp[j] = exps[j]-'0';
j++; // 2
}
count = i; // 3
while(in_temp[count]<='0' && in_temp[count]<='9') {
power = (j-count)-1;
t = t + in_temp[count]*(pow(10,power));
power--;
count++;
}
in_push(eval_stack,t);
i=j-1;
t=0;
break;
case '+':
temp = pop();
pop();
result = eval_stack[temp] + eval_stack[temp+1];
in_push(eval_stack,result);
break;
case '-':
temp = pop();
pop();
result = eval_stack[temp] - eval_stack[temp+1];
in_push(eval_stack,result);
break;
case '*':
temp = pop();
pop();
result = eval_stack[temp] * eval_stack[temp+1];
in_push(eval_stack,result);
break;
case '/':
temp = pop();
pop();
result = eval_stack[temp] / eval_stack[temp+1];
in_push(eval_stack,result);
break;
case '^':
temp = pop();
pop();
result = pow(eval_stack[temp],eval_stack[temp+1]);
in_push(eval_stack,result);
break;
}
}
return eval_stack[top];
}
int prec(char a) {
if(a=='^')
return 3;
else if(a=='*' || a=='/' || a=='%')
return 2;
else if(a=='+' || a=='-')
return 1;
else if(a=='(')
return 0;
else
return -1;
}
void push(char stack[], char ele) {
if(top>=MAX) {
printf("\nStack Overflow");
exit(1);
}
stack[++top] = ele;
}
void in_push(double stack[], double ele) {
if(top>=MAX) {
printf("\nStack Overflow");
exit(1);
}
stack[++top] = ele;
}
int pop() {
if(top<0) {
printf("\nStack Underflow");
exit(1);
}
top = top - 1;
return top;
}
答案 3 :(得分：0)
这是我将中缀转换为后缀表达式的实现
//Infix to Postfix conversion
#include <bits/stdc++.h>
using namespace std;
bool isoperator(char c) // function to check if the character is an operator
{
if(c=='+'||c=='-'||c=='*'||c=='/'||c=='^')
return true;
else
return false;
}
int precedence(char c) // function to given the precedence of the operators
{
if(c == '^')
return 3;
else if(c == '*' || c == '/')
return 2;
else if(c == '+' || c == '-')
return 1;
else
return -1;
}
void infixToPostfix(string s) // funtion to convert infix to postfix
{
stack<char>st;
string postfix;
for(int i=0;i<s.length();i++)
{
if((s[i]>='a'&&s[i]<='z')||(s[i]>='A'&&s[i]<='Z')) // if the given character is alphabet add it to the postfix string
postfix+=s[i];
else if(s[i]=='(') // if the given character is "(" add it to the postfix string
st.push('(');
else if(s[i]==')') // if we find a closing bracket we pop everything from stack till opening bracket and add it to postfix string
{
while(st.top()=='(' && !st.empty())
{
postfix+=st.top();
st.pop();
}
if(st.top()=='(') // popping the opening bracket
st.pop();
}
else if(isoperator(s[i])) // if we find a operator
{
if(st.empty()) // if stack is empty add it to the stack
st.push(s[i]);
else
{
if(precedence(s[i])>precedence(st.top())) // if operator precedence is grater push it in stack
st.push(s[i]);
else if((precedence(s[i])==precedence(st.top()))&&(s[i]=='^')) // unique case for ^ operator
st.push(s[i]);
else
{
while((!st.empty())&&(precedence(s[i])<=precedence(st.top()))) // if precedence of st.top() is greater than s[i] adding it the postfix string
{
postfix+=st.top();
st.pop();
}
st.push(s[i]); // pushing s[i] in the stack
}
}
}
}
while(!st.empty()) // popping the remaining items from the stack and adding it to the postfix string
{
postfix+=st.top();
st.pop();
}
cout<<postfix<<endl; // printing the postfix string
}
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(NULL);
string s;
cin>>s;
infixToPostfix(s);
return 0;
}
示例：
输入：a + b *（c ^ d-e）^（f + g * h）-i
输出： abcd ^ efgh * + i-（^-（* +
ps：如果发现任何错误，请在下面评论：）
答案 4 :(得分：-2)
操作符优先级是这种情况下的问题。正确的运算符优先级按降序排列：
mul, div, mod << *, /, % >>
add, sub << +, - >>
XOR << ^ >>
在上面的问题中考虑优先功能
bool ArithmeticExpression::precedence(char operator1, char operator2)
{
if ( operator1 == '^' )
return true;
else if ( operator2 == '^' )
return false;
else if ( operator1 == '*' || operator1 == '/' )
return true;
else if ( operator1 == '+' || operator1 == '-' )
if ( operator2 == '*' || operator2 == '/' )
return false;
else
return true;
return false;
}
应根据上面提到的OPERATOR PRECEDENCE TABLE检查operator2的对应值是否优先。没有适当的比较，不要返回任何值。