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February 14, 2022 08:46
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MathParser.cs
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// <expression> -> <term> (("+" | "-") <term>)* | |
// <term> -> <power> (("*" | "/") <power>)* | |
// <power> -> <unary> ("^" <power>)* | |
// <unary> -> ("-")? <unary> | <factor> | |
// <factor> -> NUMBER | "(" <expression> ")" | |
class Program { | |
public static void Main(String[] args) { | |
Program p = new Program("3"); | |
Console.ReadLine(); | |
} | |
int Token; | |
string Source; | |
public Program(string source) { | |
Source = source; | |
Token = 0; | |
Console.WriteLine("Result: " + Expression()); | |
} | |
char Current() { | |
if (Token >= Source.Length) { | |
return '\0'; | |
} | |
return Source[Token]; | |
} | |
void SkipWhitespace() { | |
char c = Current(); | |
while (c == ' ' || c == '\t' || c == '\r' || c == '\n') { | |
Token++; | |
c = Current(); | |
} | |
} | |
double Expression() { | |
// <expression> -> <term> (("+" | "-") <term>)* | |
double left = Term(); | |
SkipWhitespace(); | |
char c = Current(); | |
while (c == '+' || c == '-') { | |
Token++; // Eat + or - | |
double right = Term(); | |
if (c == '+') { | |
left = left + right; | |
} else if (c == '-') { | |
left = left - right; | |
} | |
SkipWhitespace(); | |
c = Current(); | |
} | |
return left; | |
} | |
double Term() { | |
// <term> -> <power> (("*" | "/") <power>)* | |
double left = Power(); | |
SkipWhitespace(); | |
char c = Current(); | |
while (c == '*' || c == '/') { | |
Token++; // Eat * or / | |
double right = Power(); | |
if (c == '*') { | |
left = left * right; | |
} | |
else if (c == '/') { | |
left = left / right; | |
} | |
SkipWhitespace(); | |
c = Current(); | |
} | |
return left; | |
} | |
double Power() { | |
// <power> -> <unary> ("^" <power>)* | |
double factor = Unary(); | |
SkipWhitespace(); | |
char c = Current(); | |
if (c == '^') { | |
Token++; // Eat ^ | |
double power = Power(); | |
return Math.Pow(factor, power); | |
} | |
return factor; | |
} | |
double Unary() { | |
// <unary> -> ("-")? <unary> | <factor> | |
SkipWhitespace(); | |
char c = Current(); | |
if (c == '-') { | |
Token++; // Eat negative | |
return -1.0 * Unary(); | |
} | |
return Factor(); | |
} | |
double Factor() { | |
SkipWhitespace(); | |
char c = Current(); | |
if (c == '(') { | |
Token++; // Eat ( | |
double expr = Expression(); | |
SkipWhitespace(); | |
c = Current(); | |
if (c != ')') { | |
throw new Exception("Invalid expression in factor"); | |
} | |
Token++; // Eat ) | |
return expr; | |
} | |
return Number(); | |
} | |
double Number() { | |
SkipWhitespace(); | |
char c = Current(); | |
if (c >= '0' && c <= '9') { | |
string tmp = String.Empty; | |
while (c >= '0' && c <= '9') { | |
tmp += c.ToString(); | |
Token++; | |
c = Current(); | |
} | |
if (c == '.') { | |
tmp += c.ToString(); | |
Token++; // Eat . | |
c = Current(); | |
if (c >= '0' && c <= '9') { | |
while (c >= '0' && c <= '9') { | |
tmp += c.ToString(); | |
Token++; | |
c = Current(); | |
} | |
} | |
else { | |
throw new Exception("Invalid number format"); | |
} | |
} | |
return Double.Parse(tmp); | |
} | |
throw new Exception("Invalid number"); | |
} | |
} |
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