TheGameCreators - CodeBase - C++ Expression Evaluation Function

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Category: Math / Physics

Version: 1.0

Information

Uploaded: 26th Oct 2010 15:23

Modified: 26th Oct 2010 15:26

Author: Nizze

Summary

An evaluation function which takes a string with a mathematical expression and calculates it.

Full Description

An evaluation function which takes a string with a mathematical expression and calculates it. It also includes a few other functions that the main function uses. Feel free to use them too, but the string class itself has a few almost identical which might be quicker to use though. To use it, call Evaluate(std::string expression). It returns the result as a float. These are the operators it can take: Arithmetic: * - Multiplication / - Division + - Addition - - Subtraction (or a negative number if given only a right value) ^ - Exponentiation Boolean: = - Equal > - Greater than < - Less than ! - Not Note that the only operator that can take only a right value is -, which then means a negative number. For instance, !5 isn't valid, and will only result in 0, even if it's !0. -4+3, however, is valid, and results in -1.

C++ Source Code

` This code was downloaded from The Game Creators

` It is reproduced here with full permission

` http://www.thegamecreators.com

#include <stdio.h>

#include <stdlib.h>

#include <iostream>

#include <string.h>

#include <math.h>

#define Operators(C) (C=='*' || C=='/' || C=='+' || C=='-' || C=='=' || C=='>' || C=='<' || C=='&' || C=='|' || C=='!' || C=='^')

using namespace std;

string GetSubString(string Text,int Start,int End) {

string SubStringData="";

for(int c=0; c<Text.length(); c++) {

if(c>=Start && c<=End) {

char buffer[2];

buffer[0] = Text[c];

buffer[1] = '\0';

SubStringData.append(buffer);

}

return SubStringData;

}

string ReplaceSubString(string Text,int Start,int End,string NewText) {

string TextData = GetSubString(Text,0,Start-1);

TextData.append(NewText);

TextData.append(GetSubString(Text,End+1,Text.length()));

return TextData;

}

inline string NumberToString(float number) {

char buffer[128];

sprintf(buffer,"%f",number);

string rtrnbuffer = buffer;

return rtrnbuffer;

}

inline int FindNextOperatorPosition(string Expression) {

for(int c=0; c<Expression.length(); c++) {

if(Operators(Expression[c]) && c!=0) {

return c;

}

return Expression.length();

}

float Evaluate(string Expression) {

//Strip whitespaces

for(int c = 0; c<Expression.length(); c++) {

if(Expression[c]==' ' || Expression[c]=='\t') Expression = ReplaceSubString(Expression,c,c,"");

}

int OPPos=0;

int Pos = 0;

bool Repeat;

//Sort out paranthesis

do {

Repeat=false;

for(int c = 0; c<Expression.length(); c++) {

if(Expression[c]=='(') {

OPPos = c;

} else if(Expression[c]==')') {

Expression = ReplaceSubString(Expression,OPPos,c,NumberToString(Evaluate(GetSubString(Expression,OPPos+1,c-1))));

Repeat = true;

OPPos = 0;

break;

}

} while(Repeat);

//Handle ^

do {

Repeat=false;

for(int c = 0; c<Expression.length(); c++) {

if(Expression[c]=='^' && c!=Pos) {

float Number1 = atof(GetSubString(Expression,Pos,c-1).c_str());

string Number2s = GetSubString(Expression,c+1,Expression.length());

int EndPos = FindNextOperatorPosition(Number2s);

float Number2 = atof(GetSubString(Number2s,0,EndPos).c_str());

string Result = NumberToString((float)pow((int)Number1,(int)Number2));

Expression = ReplaceSubString(Expression,Pos,EndPos+c,Result);

Repeat=true;

break;

} else if(Operators(Expression[c]) && c!=Pos) Pos=c+1;

}

} while(Repeat);

Pos=0;

//Handle *,/,

do {

Repeat=false;

for(int c = 0; c<Expression.length(); c++) {

if(Expression[c]=='*' && c!=Pos) {

float Number1 = atof(GetSubString(Expression,Pos,c-1).c_str());

string Number2s = GetSubString(Expression,c+1,Expression.length());

int EndPos = FindNextOperatorPosition(Number2s);

float Number2 = atof(GetSubString(Number2s,0,EndPos).c_str());

string Result = NumberToString(Number1*Number2);

Expression = ReplaceSubString(Expression,Pos,EndPos+c,Result);

Repeat=true;

break;

} else if(Expression[c]=='/' && c!=Pos) {

float Number1 = atof(GetSubString(Expression,Pos,c-1).c_str());

string Number2s = GetSubString(Expression,c+1,Expression.length());

int EndPos = FindNextOperatorPosition(Number2s);

float Number2 = atof(GetSubString(Number2s,0,EndPos).c_str());

string Result = NumberToString(Number1/Number2);

Expression = ReplaceSubString(Expression,Pos,EndPos+c,Result);

Repeat=true;

break;

} else if(Operators(Expression[c]) && c!=Pos) Pos=c+1;

}

} while(Repeat);

Pos=0;

//Handle + and -

do {

Repeat=false;

for(int c = 0; c<Expression.length(); c++) {

if(Expression[c]=='+' && c!=Pos) {

float Number1 = atof(GetSubString(Expression,Pos,c-1).c_str());

string Number2s = GetSubString(Expression,c+1,Expression.length());

int EndPos = FindNextOperatorPosition(Number2s);

float Number2 = atof(GetSubString(Number2s,0,EndPos).c_str());

string Result = NumberToString(Number1+Number2);

Expression = ReplaceSubString(Expression,Pos,EndPos+c,Result);

Repeat=true;

break;

} else if(Expression[c]=='-' && c!=Pos) {

float Number1 = atof(GetSubString(Expression,Pos,c-1).c_str());

string Number2s = GetSubString(Expression,c+1,Expression.length());

int EndPos = FindNextOperatorPosition(Number2s);

float Number2 = atof(GetSubString(Number2s,0,EndPos).c_str());

string Result = NumberToString(Number1-Number2);

Expression = ReplaceSubString(Expression,Pos,EndPos+c,Result);

Repeat=true;

break;

} else if(Operators(Expression[c]) && c!=Pos) Pos=c+1;

}

} while(Repeat);

Pos=0;

//Handle =,>,<, and !

do {

Repeat=false;

for(int c = 0; c<Expression.length(); c++) {

if(Expression[c]=='=' && c!=Pos) {

float Number1 = atof(GetSubString(Expression,Pos,c-1).c_str());

string Number2s = GetSubString(Expression,c+1,Expression.length());

int EndPos = FindNextOperatorPosition(Number2s);

float Number2 = atof(GetSubString(Number2s,0,EndPos).c_str());

string Result = NumberToString(Number1==Number2);

Expression = ReplaceSubString(Expression,Pos,EndPos+c,Result);

Repeat=true;

break;

} else if(Expression[c]=='<' && c!=Pos) {

float Number1 = atof(GetSubString(Expression,Pos,c-1).c_str());

string Number2s = GetSubString(Expression,c+1,Expression.length());

int EndPos = FindNextOperatorPosition(Number2s);

float Number2 = atof(GetSubString(Number2s,0,EndPos).c_str());

string Result = NumberToString(Number1<Number2);

/*string Result;

if(Number1<Number2) Result="1";

else Result="0";*/

Expression = ReplaceSubString(Expression,Pos,EndPos+c,Result);

Repeat=true;

break;

} else if(Expression[c]=='>' && c!=Pos) {

float Number1 = atof(GetSubString(Expression,Pos,c-1).c_str());

string Number2s = GetSubString(Expression,c+1,Expression.length());

int EndPos = FindNextOperatorPosition(Number2s);

float Number2 = atof(GetSubString(Number2s,0,EndPos).c_str());

string Result = NumberToString(Number1>Number2);

/*string Result;

if(Number1>Number2) Result="1";

else Result="0";*/

Expression = ReplaceSubString(Expression,Pos,EndPos+c,Result);

Repeat=true;

break;

} else if(Expression[c]=='!' && c!=Pos) {

float Number1 = atof(GetSubString(Expression,Pos,c-1).c_str());

string Number2s = GetSubString(Expression,c+1,Expression.length());

int EndPos = FindNextOperatorPosition(Number2s);

float Number2 = atof(GetSubString(Number2s,0,EndPos).c_str());

string Result = NumberToString(Number1!=Number2);

/*string Result;

if(Number1>Number2) Result="1";

else Result="0";*/

Expression = ReplaceSubString(Expression,Pos,EndPos+c,Result);

Repeat=true;

break;

} else if(Operators(Expression[c]) && c!=Pos) Pos=c+1;

}

} while(Repeat);

Pos=0;

//Handle | and &

do {

Repeat=false;

for(int c = 0; c<Expression.length(); c++) {

if(Expression[c]=='&' && c!=0) {

float Number1 = atof(GetSubString(Expression,Pos,c-1).c_str());

string Number2s = GetSubString(Expression,c+1,Expression.length());

int EndPos = FindNextOperatorPosition(Number2s);

float Number2 = atof(GetSubString(Number2s,0,EndPos).c_str());

string Result = NumberToString((Number1 && Number2));

Expression = ReplaceSubString(Expression,Pos,EndPos+c,Result);

Repeat=true;

break;

} else if(Expression[c]=='|' && c!=0) {

float Number1 = atof(GetSubString(Expression,Pos,c-1).c_str());

string Number2s = GetSubString(Expression,c+1,Expression.length());

int EndPos = FindNextOperatorPosition(Number2s);

float Number2 = atof(GetSubString(Number2s,0,EndPos).c_str());

string Result = NumberToString((Number1 || Number2));

Expression = ReplaceSubString(Expression,Pos,EndPos+c,Result);

Repeat=true;

break;

} else if(Operators(Expression[c]) && c!=0) Pos=c+1;

}

} while(Repeat);

return atof(Expression.c_str());

}

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Author Name:	Nizze
CodeBase Entries:	1

CodeBase - C++ Expression Evaluation Function

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