An extensible math expression parser with plug-ins

#include "MTCommon.h"
#include <windows.h>

bool findSubStr(const MTSTRING &str, const MTSTRING &subStr)
{
	int strLength = str.size();
	int subStrLength = subStr.size();

	if( subStrLength > strLength )
	{
		return false;	
	}

	int end = strLength - subStrLength;

	for( int t=0; t<=end; t++ )
	{
		if( isStrBegin(str.c_str()+t, subStr.c_str(), strLength-t, subStrLength ) )
		{
			return true;
		}

	}

	return false;
}

bool isStrBegin(const MTCHAR *str, const MTCHAR *beginStr, int strLength, int beginStrLength)
{
	if( strLength == -1 )
	{
		strLength = lstrlen(str);
	}

	if( beginStrLength == -1 )
	{
		beginStrLength = lstrlen(beginStr);
	}
	
	if( beginStrLength > strLength )
	{
		return false;	// impossible to find a substring that is lengthier than the string itself!
	}

	for(int pos=0; pos < beginStrLength; pos++ )
	{
		if( str[pos] != beginStr[pos] )
		{
			return false;	// no match...!
		}
	}

	return true;	// match!

}

// check if this word contains only numerical characters
bool isOnlyNum(const MTCHAR *word, const MTCHAR &decimalPoint)
{	
	unsigned int length = lstrlen(word);
	bool decimal = false;	// indicate if a decimal point character has been encountered
							// at most it can only have one decimal point character
							// else, this is not a numerical only string

	for( unsigned int t=0; t<length; t++ )
	{
		// if this is not a numeric character and not the decimal point character
		if( !MTISDIGIT(word[t]) && word[t] != decimalPoint )
		{
			return false;	// alpha or special character
		}

		if( word[t] == decimalPoint )
		{
			if( decimal )
			{
				return false;	// a second decimal point character! 			
			}
			else
			{
				decimal = true;
			}

		}
			

	}

	return true;
}