[英]C++ infix to postfix
编译时出现以下错误:
convert.cpp: In function 'std::string convert()':
convert.cpp:62: error: expected primary-expression before 'else'
convert.cpp:62: error: expected `;' before 'else'
convert.cpp:108: error: expected `}' at end of input
convert.cpp:108: error: expected `}' at end of input
convert.cpp:108: error: expected `}' at end of input
convert.cpp:108: error: expected `}' at end of input
convert.cpp:108: error: expected `}' at end of input
码:
#include<iostream>
#include<stack>
#include<string>
using namespace std;
string infix; // infix expression string
string operand;
string operate;
stack <string> mystack; // this stack is used to push the operator
string postfix; // postfix string where the operand is appended
//....................................................................
// this function read the infix expression from user
string input()
{
cout<<" Enter the damn infix expression: "<<endl;
getline(cin, infix);
return infix;
}
//......................................................................
// this function checks for operator precedence in the stack
int precedence(string e)
{
int f;
if(e == "*" || e== "/" || e =="%")
f = 2;
else
{
if(e == "+" || e == "-")
f = 1;
}
if(e=="."){
f=0;
}
return f;
}
//....................................................................
// This function converts infix to postfix
string convert()
{
for(int i=0; i<infix.length(); i++)
{
switch(infix[i]){
// operate case start
case '+': case'-': case'*': case'/': case'^': case '(': case ')': case'.':
operate=infix[i];
{
if(mystack.empty() || precedence(operate)>= precedence(mystack.top()))
{
mystack.push(operate);
else
{
while(precedence(operate)<= precedence(mystack.top()))
{
postfix.append(mystack.top());
mystack.pop();
}
mystack.push(operate);
}
}
}//operate case closed
default: //when operand string char is parsed
{
operand=infix[i];
postfix.append(operand);
break;
} // default case closed
}//switch closed
}
while(!mystack.empty())
{
postfix.append(mystack.top())
mystack.pop();
}
return postfix;
cout<<postfix;
}
//...................................................................
int main()
{
input();
convert();
cout<<"postfix is "<<postfix<<endl;
}
看来您的代码只是缺少一些右花括号。 就这样。
例如,看这个:
operate=infix[i];
{
if(mystack.empty() || precedence(operate)>= precedence(mystack.top()))
{
mystack.push(operate);
else
{
while(precedence(operate)<= precedence(mystack.top()))
else语句前的结束}在哪里。 只需检查您的代码并修复这些愚蠢的错误即可。
这将是一个更容易摆脱这些事情你自己,如果你做了空格和缩进一点点整洁。
“在其他情况之前预期的主要表达”诊断是编译器作者向您粗鲁地向您报告“其他”而没有前面的“ if”或“ else if”的方式。 Alexander Rafferty正确地指出这是因为代码具有...
if (condition) {
// ...
else { }
...当你的意思是...
if (condition) {
// ...
}
else {
}
……尽管也许您是偶然删除了一大堆东西,并且很幸运地删除了这些代码,导致代码无法解析,所以您将意识到有些错误。
看一下这些行:
if(mystack.empty() || precedence(operate)>= precedence(mystack.top()))
{
mystack.push(operate);
else
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