如何创建一个可以计算任意长表达式的计算器表达式？ [英] How can create a calculator expression that can calculate an arbitary long expression ?
问题描述
样本
pi = 3.14 radius = 3 sin（pi / 2）+ pi * radius ^ 2 + 0x1F - 1100b
由于二进制文件会出错和十六进制数。
我尝试过：
sample
pi = 3.14 radius = 3 sin( pi / 2 ) + pi * radius ^ 2 + 0x1F - 1100b
it will give error due to the binary and hexadecimal numbers.
What I have tried:
#include "parser.h"
// returns a number from 0 up to, but excluding x
const int getrandom (const int x)
{
if (x <= 0)
return 0;
// r will be between 0 and 1 (but below 1 as we are dividing by RAND_MAX+1)
double r = static_cast<double> (std::rand () % RAND_MAX) / (static_cast<double> (RAND_MAX) + 1.0);
return floor (r * x);
} // end of getrandom
const int roll (const int howmany, const int die)
{
int count;
int total = 0;
for (count = 0; count < howmany; ++count)
total += getrandom (die) + 1;
return total;
} // end of roll
// returns true if a x% probability exists
// eg. percent (80) will be true 80% of the time
static int initRandom ()
{
srand (time (NULL));
#ifndef WIN32
srand48 (time (NULL));
#endif
return 0;
}
// initialise random number generator
static int someNumber = initRandom ();
// functions we can call from an expression
double DoInt (double arg)
{
return (double) arg; // drop fractional part
}
double toInteger(char c)
{
if (c >= '0' && c <= '9') return c -'0';
if (c >= 'a' && c <= 'f') return c -'a' + 0xa;
if (c >= 'A' && c <= 'F') return c -'A' + 0xa;
double noDigit = 0xf + 1;
return noDigit;
}
double toHex(char c)
{
return (std::tolower(c) == 'x' && toInteger(c) <= 0xf);
}
double DoRandom (double arg)
{
return getrandom (static_cast <double> (arg)); // random number in range 0 to arg
}
const double DoIf (const double arg1, const double arg2, const double arg3)
{
if (arg1 != 0.0)
return arg2;
else
return arg3;
}
typedef double (*OneArgFunction) (double arg);
typedef const double (*TwoArgFunction) (const double arg1, const double arg2);
typedef const double (*ThreeArgFunction) (const double arg1, const double arg2, const double arg3);
// maps of function names to functions
static std::map<std::string, OneArgFunction> OneArgumentFunctions;
static std::map<std::string, TwoArgFunction> TwoArgumentFunctions;
static std::map<std::string, ThreeArgFunction> ThreeArgumentFunctions;
// for standard library functions
#define STD_FUNCTION(arg) OneArgumentFunctions [#arg] = arg
static int LoadOneArgumentFunctions ()
{
OneArgumentFunctions ["abs"] = fabs;
STD_FUNCTION (acos);
STD_FUNCTION (asin);
STD_FUNCTION (atan);
#ifndef WIN32 // doesn't seem to exist under Visual C++ 6
STD_FUNCTION (atanh);
#endif
//STD_FUNCTION (ceil);
STD_FUNCTION (cos);
//STD_FUNCTION (cosh);
STD_FUNCTION (exp);
STD_FUNCTION (exp);
// STD_FUNCTION (floor);
STD_FUNCTION (log);
STD_FUNCTION (log10);
STD_FUNCTION (sin);
//STD_FUNCTION (sinh);
STD_FUNCTION (sqrt);
STD_FUNCTION (tan);
//STD_FUNCTION (tanh);
OneArgumentFunctions ["int"] = DoInt;
OneArgumentFunctions ["rand"] = DoRandom;
OneArgumentFunctions ["rand"] = DoRandom;
// OneArgumentFunctions ["percent"] = DoPercent;
return 0;
} // end of LoadOneArgumentFunctions
static int LoadThreeArgumentFunctions ()
{
ThreeArgumentFunctions ["if"] = DoIf;
return 0;
} // end of LoadThreeArgumentFunctions
const Parser::TokenType Parser::GetToken (const bool ignoreSign)
{
word_.erase (0, std::string::npos);
// skip spaces
while (*pWord_ && isspace (*pWord_))
++pWord_;
pWordStart_ = pWord_; // remember where word_ starts *now*
// look out for unterminated statements and things
if (*pWord_ == 0 && // we have EOF
type_ == END) // after already detecting it
throw std::runtime_error ("Unexpected end of expression.");
unsigned char cFirstCharacter = *pWord_; // first character in new word_
if (cFirstCharacter == 0) // stop at end of file
{
word_ = "<end of expression>";
return type_ = END;
}
unsigned char cNextCharacter = *(pWord_ + 1); // 2nd character in new word_
// look for number
// can be: + or - followed by a decimal point
// or: + or - followed by a digit
// or: starting with a digit
// or: decimal point followed by a digit
if ((!ignoreSign &&
(cFirstCharacter == '+' || cFirstCharacter == '-') &&
(isdigit (cNextCharacter) || cNextCharacter == '.')
)
|| isdigit (cFirstCharacter)
// allow decimal numbers without a leading 0. e.g. ".5"
|| (cFirstCharacter == '.' && isdigit (cNextCharacter)) )
{
// skip sign for now
if ((cFirstCharacter == '+' || cFirstCharacter == '-'))
pWord_++;
while (isdigit (*pWord_) || *pWord_ == '.')
pWord_++;
// allow for 1.53158e+15
if (*pWord_ == 'e' || *pWord_ == 'E')
{
pWord_++; // skip 'e'
if ((*pWord_ == '+' || *pWord_ == '-'))
pWord_++; // skip sign after e
while (isdigit (*pWord_)) // now digits after e
pWord_++;
}
word_ = std::string (pWordStart_, pWord_ - pWordStart_);
std::istringstream is (word_);
// parse std::string into double value
is >> value_;
if (is.fail () && !is.eof ())
throw std::runtime_error ("Bad numeric literal: " + word_);
return type_ = NUMBER;
} // end of number found
// special test for 2-character sequences: <= >= == !=
// also +=, -=, /=, *=
if (cNextCharacter == '=')
{
switch (cFirstCharacter)
{
// comparisons
case '=': type_ = EQ; break;
case '<': type_ = LE; break;
case '>': type_ = GE; break;
case '!': type_ = NE; break;
// assignments
case '+': type_ = ASSIGN_ADD; break;
case '-': type_ = ASSIGN_SUB; break;
case '*': type_ = ASSIGN_MUL; break;
case '/': type_ = ASSIGN_DIV; break;
// none of the above
default: type_ = NONE; break;
} // end of switch on cFirstCharacter
if (type_ != NONE)
{
word_ = std::string (pWordStart_, 2);
pWord_ += 2; // skip both characters
return type_;
} // end of found one
} // end of *=
switch (cFirstCharacter)
{
case '&': if (cNextCharacter == '&') // &&
{
word_ = std::string (pWordStart_, 2);
pWord_ += 2; // skip both characters
return type_ = AND;
}
break;
case '|': if (cNextCharacter == '|') // ||
{
word_ = std::string (pWordStart_, 2);
pWord_ += 2; // skip both characters
return type_ = OR;
}
break;
// single-character symboles
case '=':
case '<':
case '>':
case '+':
case '-':
case '/':
case '*':
case '(':
case ')':
case ',':
case '!':
word_ = std::string (pWordStart_, 1);
++pWord_; // skip it
return type_ = TokenType (cFirstCharacter);
} // end of switch on cFirstCharacter
if (!isalpha (cFirstCharacter))
{
if (cFirstCharacter < ' ')
{
std::ostringstream s;
s << "Unexpected character (decimal " << int (cFirstCharacter) << ")";
throw std::runtime_error (s.str ());
}
else
throw std::runtime_error ("Unexpected character: " + std::string (1, cFirstCharacter));
}
// we have a word (starting with A-Z) - pull it out
while (isalnum (*pWord_) || *pWord_ == '_')
++pWord_;
word_ = std::string (pWordStart_, pWord_ - pWordStart_);
return type_ = NAME;
} // end of Parser::GetToken
// force load of functions at static initialisation time
static int doLoadOneArgumentFunctions = LoadOneArgumentFunctions ();
//static int doLoadTwoArgumentFunctions = LoadTwoArgumentFunctions ();
static int doLoadThreeArgumentFunctions = LoadThreeArgumentFunctions ();
const double Parser::Primary (const bool get) // primary (base) tokens
{
if (get)
GetToken (); // one-token lookahead
switch (type_)
{
case NUMBER:
{
double v = value_;
GetToken (true); // get next one (one-token lookahead)
return v;
}
case 0xf :
{
if( type_==0xf){
GetToken(true);
return value_;
}
}
case NAME:
{
std::string word = word_;
GetToken (true);
if (type_ == LHPAREN)
{
// might be single-argument function (eg. abs (x) )
std::map<std::string, OneArgFunction>::const_iterator si;
si = OneArgumentFunctions.find (word);
if (si != OneArgumentFunctions.end ())
{
double v = Expression (true); // get argument
CheckToken (RHPAREN);
GetToken (true); // get next one (one-token lookahead)
return si->second (v); // evaluate function
}
// might be double-argument function (eg. roll (6, 2) )
std::map<std::string, TwoArgFunction>::const_iterator di;
di = TwoArgumentFunctions.find (word);
if (di != TwoArgumentFunctions.end ())
{
double v1 = Expression (true); // get argument 1 (not commalist)
CheckToken (COMMA);
double v2 = Expression (true); // get argument 2 (not commalist)
CheckToken (RHPAREN);
GetToken (true); // get next one (one-token lookahead)
return di->second (v1, v2); // evaluate function
}
// might be double-argument function (eg. roll (6, 2) )
std::map<std::string, ThreeArgFunction>::const_iterator ti;
ti = ThreeArgumentFunctions.find (word);
if (ti != ThreeArgumentFunctions.end ())
{
double v1 = Expression (true); // get argument 1 (not commalist)
CheckToken (COMMA);
double v2 = Expression (true); // get argument 2 (not commalist)
CheckToken (COMMA);
double v3 = Expression (true); // get argument 3 (not commalist)
CheckToken (RHPAREN);
GetToken (true); // get next one (one-token lookahead)
return ti->second (v1, v2, v3); // evaluate function
}
throw std::runtime_error ("Function '" + word + "' not implemented.");
}
// not a function? must be a symbol in the symbol table
double & v = symbols_ [word]; // get REFERENCE to symbol table entry
// change table entry with expression? (eg. a = 22, or a = 22)
switch (type_)
{
// maybe check for NaN or Inf here (see: isinf, isnan functions)
case ASSIGN: v = Expression (true); break;
case ASSIGN_ADD: v += Expression (true); break;
case ASSIGN_SUB: v -= Expression (true); break;
case ASSIGN_MUL: v *= Expression (true); break;
case ASSIGN_DIV:
{
double d = Expression (true);
if (d == 0.0)
throw std::runtime_error ("Divide by zero");
v /= d;
break; // change table entry with expression
} // end of ASSIGN_DIV
default: break; // do nothing for others
} // end of switch on type_
return v; // and return new value
}
case MINUS: // unary minus
return - Primary (true);
case NOT: // unary not
return (Primary (true) == 0.0) ? 1.0 : 0.0;;
case LHPAREN:
{
double v = CommaList (true); // inside parens, you could have commas
CheckToken (RHPAREN);
GetToken (true); // eat the )
return v;
}
default:
throw std::runtime_error ("Unexpected token: " + word_);
} // end of switch on type
} // end of Parser::Primary
const double Parser::Term (const bool get) // multiply and divide
{
double left = Primary (get);
while (true)
{
switch (type_)
{
case MULTIPLY:
left *= Primary (true); break;
case DIVIDE:
{
double d = Primary (true);
if (d == 0.0)
throw std::runtime_error ("Divide by zero");
left /= d;
break;
}
default: return left;
} // end of switch on type
} // end of loop
} // end of Parser::Term
const double Parser::AddSubtract (const bool get) // add and subtract
{
double left = Term (get);
while (true)
{
switch (type_)
{
case PLUS: left += Term (true); break;
case MINUS: left -= Term (true); break;
default: return left;
} // end of switch on type
} // end of loop
} // end of Parser::AddSubtract
const double Parser::Comparison (const bool get) // LT, GT, LE, EQ etc.
{
double left = AddSubtract (get);
while (true)
{
switch (type_)
{
case LT: left = left < AddSubtract (true) ? 1.0 : 0.0; break;
case GT: left = left > AddSubtract (true) ? 1.0 : 0.0; break;
case LE: left = left <= AddSubtract (true) ? 1.0 : 0.0; break;
case GE: left = left >= AddSubtract (true) ? 1.0 : 0.0; break;
case EQ: left = left == AddSubtract (true) ? 1.0 : 0.0; break;
case NE: left = left != AddSubtract (true) ? 1.0 : 0.0; break;
default: return left;
} // end of switch on type
} // end of loop
} // end of Parser::Comparison
const double Parser::Expression (const bool get) // AND and OR
{
double left = Comparison (get);
while (true)
{
switch (type_)
{
case AND:
{
double d = Comparison (true); // don't want short-circuit evaluation
left = (left != 0.0) && (d != 0.0);
}
break;
case OR:
{
double d = Comparison (true); // don't want short-circuit evaluation
left = (left != 0.0) || (d != 0.0);
}
break;
default: return left;
} // end of switch on type
} // end of loop
} // end of Parser::Expression
const double Parser::CommaList (const bool get) // expr1, expr2
{
double left = Expression (get);
while (true)
{
switch (type_)
{
case COMMA: left = Expression (true); break; // discard previous value
default: return left;
} // end of switch on type
} // end of loop
} // end of Parser::CommaList
const double Parser::Evaluate () // get result
{
pWord_ = program_.c_str ();
type_ = NONE;
double v = CommaList (true);
if (type_ != END)
throw std::runtime_error ("Unexpected text at end of expression: " + std::string (pWordStart_));
return v;
}
// change program and evaluate it
const double Parser::Evaluate (const std::string & program) // get result
{
program_ = program;
return Evaluate ();
}推荐答案
Nobody is going to wade through that much code in search of a vague error like \"it will give error due to the binary and hexadecimal numbers.\"
You need to remember that compiling does not mean your code is right! ：笑：
将开发过程想象成编写电子邮件：成功编译意味着您使用正确的语言编写电子邮件 - 例如英语而不是德语 - 而不是电子邮件包含您的邮件想发送。
所以现在你进入第二阶段的发展（实际上它是第四或第五阶段，但你将在之后的阶段进入）：测试和调试。
首先查看它的作用，以及它与你想要的有何不同。这很重要，因为它可以为您提供有关其原因的信息。例如，如果程序旨在让用户输入一个数字并将其翻倍并打印答案，那么如果输入/输出是这样的：
Nobody is going to wade through that much code in search of a vague error like "it will give error due to the binary and hexadecimal numbers."
You need to remember that compiling does not mean your code is right! :laugh:
Think of the development process as writing an email: compiling successfully means that you wrote the email in the right language - English, rather than German for example - not that the email contained the message you wanted to send.
So now you enter the second stage of development (in reality it's the fourth or fifth, but you'll come to the earlier stages later): Testing and Debugging.
Start by looking at what it does do, and how that differs from what you wanted. This is important, because it give you information as to why it's doing it. For example, if a program is intended to let the user enter a number and it doubles it and prints the answer, then if the input / output was like this:
Input Expected output Actual output
1 2 1
2 4 4
3 6 9
4 8 16然后很明显问题出在将它加倍的位 - 它不会将自身加到自身上，或者将它乘以2，它会将它自身相乘并返回输入的平方。
所以，你可以查看代码和很明显，它在某处：
Then it's fairly obvious that the problem is with the bit which doubles it - it's not adding itself to itself, or multiplying it by 2, it's multiplying it by itself and returning the square of the input.
So with that, you can look at the code and it's obvious that it's somewhere here:
int Double(int value)
{
return value * value;
}
一旦你知道可能出现的问题，就开始使用调试器找出原因。在方法的第一行放置一个断点，然后运行你的应用程序。当它到达断点时，调试器将停止，并将控制权移交给您。您现在可以逐行运行代码（称为单步执行）并根据需要查看（甚至更改）变量内容（哎呀，您甚至可以更改代码并在需要时再试一次）。 />
在执行代码之前，请考虑代码中的每一行应该做什么，并将其与使用Step over按钮依次执行每一行时实际执行的操作进行比较。它符合您的期望吗？如果是这样，请转到下一行。
如果没有，为什么不呢？它有什么不同？
希望这可以帮助你找到代码的哪个部分有问题，以及问题是什么。
这是一项技能，它是一个值得开发的，因为它可以帮助你在现实世界和发展中。 And like all skills, it only improves by use!
Once you have an idea what might be going wrong, start using the debugger to find out why. Put a breakpoint on the first line of the method, and run your app. When it reaches the breakpoint, the debugger will stop, and hand control over to you. You can now run your code line-by-line (called "single stepping") and look at (or even change) variable contents as necessary (heck, you can even change the code and try again if you need to).
Think about what each line in the code should do before you execute it, and compare that to what it actually did when you use the "Step over" button to execute each line in turn. Did it do what you expect? If so, move on to the next line.
If not, why not? How does it differ?
Hopefully, that should help you locate which part of that code has a problem, and what the problem is.
This is a skill, and it's one which is well worth developing as it helps you in the real world as well as in development. And like all skills, it only improves by use!
it will give error due to the binary and hexadecimal numbers.
it will give error due to the binary and hexadecimal numbers.
Your code do not behave the way you expect, or you don’t understand why !
There is an almost universal solution: Run your code on debugger step by step, inspect variables.
The debugger is here to show you what your code is doing and your task is to compare with what it should do.
There is no magic in the debugger, it don’t know what your code is supposed to do, it don’t find bugs, it just help you to by showing you what is going on.当代码没有达到预期的效果时，你就接近了一个错误。
要查看你的代码在做什么：只需设置断点并查看代码是否正常运行，调试器允许你执行第1行第1行，并在执行时检查变量。
调试器 - 维基百科，免费的百科全书 [ ^ ]
掌握调试Visual Studio 2010 - 初学者指南 [ ^ ]
使用Visual Studio 2010进行基本调试 - YouTube [ ^ ]
1.11 - 调试程序（步进和断点）| Learn C++[^]
The debugger is here to only show you what your code is doing and your task is to compare with what it should do.
Your code do not behave the way you expect, or you don't understand why !
There is an almost universal solution: Run your code on debugger step by step, inspect variables.
The debugger is here to show you what your code is doing and your task is to compare with what it should do.
There is no magic in the debugger, it don't know what your code is supposed to do, it don't find bugs, it just help you to by showing you what is going on. When the code don't do what is expected, you are close to a bug.
To see what your code is doing: Just set a breakpoint and see your code performing, the debugger allow you to execute lines 1 by 1 and to inspect variables as it execute.
Debugger - Wikipedia, the free encyclopedia[^]
Mastering Debugging in Visual Studio 2010 - A Beginner's Guide[^]
Basic Debugging with Visual Studio 2010 - YouTube[^]
1.11 — Debugging your program (stepping and breakpoints) | Learn C++[^]
The debugger is here to only show you what your code is doing and your task is to compare with what it should do.
You must write parser which firstly parses the text and than understands its logic correct.
Example: 3 * 2 + 5
first step ist finding the numbers and operators \"3\", \"*\", \"2\", \"+\" and \"5\"
than you need to concatenate them with the correct logic:(\"3\", \"*\", \"2\") and ( \"+\" ,\"5\")
than you can start the operations.
You must write parser which firstly parses the text and than understands its logic correct.
Example: 3 * 2 + 5
first step ist finding the numbers and operators "3", "*", "2", "+" and "5"
than you need to concatenate them with the correct logic:("3", "*", "2") and ( "+" ,"5")
than you can start the operations.
这篇关于如何创建一个可以计算任意长表达式的计算器表达式？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
