head.h

#include<iostream>
#include<string>
using namespace std;

class STRING
{
public:
	STRING();
	void GetString();
	void GetSubString();
	void Index();
	void Print();
private:
	void Index1();
	void Index2();
	bool Match(int);
	string str;
	string sub;
	int strlen;
	int sublen;
	int pos;
};

STRING::STRING()
{
	str.clear();
	sub.clear();
	pos = strlen = sublen = 0;
}

void STRING::GetString()
{
	cout << "Please Input The MainString :" << endl << endl;
	cin >> str;
	strlen = str.length();
}

void STRING::GetSubString()
{
	cout << "Please Input The SubString :" << endl << endl;
	cin >> sub;
	sublen = sub.length();
}

void STRING::Index()
{
	cout << "Index Called !" << endl << endl;
	cout << "Which Position Do You Want To Start Your Index ?" << endl << endl;
	cin >> pos;
	pos--;
	cout << "Which Method Do You Want To Use ?" << endl << endl;
	cout << "1 . Simple Method ." << endl << "2 . Improvement Method ." << endl
			<< endl;
	char choice;
	cin >> choice;
	switch (choice)
	{
	case '1':
		Index1();
		break;
	case '2':
		Index2();
		break;
	default:
		cout << "No Such Method !" << endl << endl;
		break;
	}
}

void STRING::Index1()
{
	cout << "Simple Method Called !" << endl << endl;
	if (pos > strlen - sublen)
	{
		cout << "Failed !" << endl << endl;
		return;
	}
	int i, j;
	i = pos;
	j = 0;
	while (i < strlen && j < sublen)
	{
		if (str[i] == sub[j])
		{
			i++;
			j++;
		}
		else
		{
			i = i - j + 1;
			j = 0;
		}
	}
	if (j == sublen)
	{
		cout << "Succed ! " << " Position = " << i - j + 1 << endl << endl;
	}
	else
	{
		cout << "Failed !" << endl << endl;
	}
}

void STRING::Index2()
{
	cout << "ImproveMent Method Called !" << endl << endl;
	int i, j;
	i = pos;
	j = 0;
	while (i <= strlen - sublen && j < sublen)
	{
		if (str[i] == sub[j] && str[i + sublen - 1] == sub[sublen - 1]
				&& Match(i))
		{
			cout << "Succed ! " << " Position = " << i - j + 1 << endl << endl;
			return;
		}
		else
		{
			i++;
			j = 0;
		}
	}
	cout << "Failed !" << endl << endl;
}

void STRING::Print()
{
	cout << "Main String = " << str << endl << " Length = " << strlen << endl;
	cout << "SubString = " << sub << endl << " Length = " << sublen << endl
			<< endl;
}

bool STRING::Match(int i)
{
	for (int j = 0; j < sublen; j++)
	{
		if (str[i + j] != sub[j])
			return false;
	}
	return true;
}

main.cpp

#include<iostream>
#include"head.h"
using namespace std;

int main()
{
	STRING str;
	char choice;
	while (1)
	{
		cout << "Your Choice Please ?" << endl << endl << "1 . Set Main String"
				<< endl << "2 . Set SubString" << endl << "3 . Index" << endl
				<< "4 . Print" << endl << "5 . Quit" << endl << endl;
		cin >> choice;
		switch (choice)
		{
		case '1':
			str.GetString();
			break;
		case '2':
			str.GetSubString();
			break;
		case '3':
			str.Index();
			break;
		case '4':
			str.Print();
			break;
		case '5':
			return 0;
		default:
			cout << "No Such Choice !" << endl;
			break;
		}
	}
}