Question 1
#include<iostream>

using namespace std;

int main(){

	string word = "Computer";
	int x;

	while (1)
	{
		do {
			cout << "Array index = ";
			cin >> x;
			if ((x < 0) || (x >=word.length()))
				printf("Out of range\n\n");
		} while ((x < 0) || (x >= word.length()));

		cout << "Content = " << word[x]<<endl;
	}



        return 0;
}

Question 2
#include<iostream>

using namespace std;

int main(){

	string sentence = "Sacred Heart Canossian College";
	int x, y, i;

	while (1)
	{
		do {
			cout << "Starting index = ";
			cin >> x;
		} while ((x < 0) || (x >= sentence.length()));

		do {
			cout << "Length of the substring = ";
			cin >> y;
		} while ((y <= 0) || (y >= sentence.length()-x+1));

		cout << "Result = ";
		for (i=x; i<x+y; i++)
			cout << sentence[i];
		cout << endl;
	}


        return 0;
}

Question 3
#include<iostream>

using namespace std;

int main(){

	string sentence;
	int count=0, i;

	cout << "Enter a sentence: ";
	getline (cin,sentence);

	if (sentence[0] != ' ')
		count++;

	for (i=1; i<sentence.length(); i++)
		if ((sentence[i-1] == ' ') && (sentence[i] != ' '))
			count++;

	cout << "Number of words = " << count << endl;

    return 0;
}

alternative answer (handle consecutive spaces)
#include<iostream>

using namespace std;

int main(){

    string sentence;
    int count = 0, i;

    cout << "Enter a sentence: ";
    getline(cin, sentence);

    bool in_word = false; //whether currently inside a word
    for (i = 0; i < sentence.length(); i++) {
        if (sentence[i] == ' ') {
            in_word = false; //end of word
        } else if (!in_word) {
            count++;
            in_word = true; //start of new word
        }
    }

    cout << "Number of words = " << count << endl;

    return 0;
}

Question 4(a)
#include<iostream>

using namespace std;

int main(){

	string sentence;
	int i;

	cout << "Enter a sentence: ";
	getline(cin,sentence);

	for (i=0; i<sentence.length(); i++)
		if ((sentence[i] >= 'a') && (sentence[i] <= 'z'))
			sentence[i] = sentence[i] - 'a' + 'A';

	cout << sentence << endl;
    return 0;
}

Question 4(b)
#include<iostream>

using namespace std;

int main(){

	string sentence;
	int i;

	cout << "Enter a sentence: ";
	getline(cin,sentence);

	for (i=0; i<sentence.length(); i++)
		if ((sentence[i] >= 'A') && (sentence[i] <= 'Z'))
			sentence[i] = sentence[i] + 'a' - 'A';

	cout << sentence << endl;
    return 0;
}


Question 4(c)
#include<iostream>

using namespace std;

int main(){

	string sentence;
	int i;

	cout << "Enter a sentence: ";
	getline(cin,sentence);

	if ((sentence[0] >= 'a') && (sentence[0] <= 'z'))
		sentence[0] = sentence[0] - 'a' + 'A';

	for (i=1; i<sentence.length(); i++)
		if ((sentence[i-1] == ' ') && (sentence[i] >= 'a') && (sentence[i] <= 'z'))
			sentence[i] = sentence[i] - 'a' + 'A';
		else if ((sentence[i-1] != ' ') && (sentence[i] >= 'A') && (sentence[i] <= 'Z'))
			sentence[i] = sentence[i] - 'A' + 'a';


	cout << sentence << endl;
    return 0;
}


Question 5
#include <iostream>

using namespace std;

int main()
{
	string s, z;
	char x[100], y[100], temp;
	int i, len;

	cout << "Plain text: ";
	getline(cin,s);

    len = s.length();
    cout << len;
	for (i=0; i<len; i++)
		x[i] = s[len-1-i];
	x[len] = '\0';

	for (i=0; i<len; i++)
		y[i] = s[i] + 1;
	y[len] = '\0';

	z = s;
	i = 0;
	while (i < len-1)
	{
		temp = z[i];
		z[i] = z[i+1];
		z[i+1] = temp;
		i = i + 2;
	}

	cout << "Cipher text (Method 1): " << x << endl;
	cout << "Cipher text (Method 2): " << y << endl;
	cout << "Cipher text (Method 3): " << z << endl;

	return 0;
}

Question 6
#include <iostream>

using namespace std;

int main()
{
	string email;
	char no[3];
	int number;

	cout << "class: ";
	cin >> email;
	cout << "number: ";
	cin >> number;

     if(email[1]>='A'&&email[1]<='Z')
     		email[1]=email[1]+('a'-'A');

	no[0] = (char) ('0' + number / 10);
	no[1] = (char) ('0' + number % 10);
	no[2] = '\0';

	email = email + no + "@shcc.edu.hk";
	
	cout << "email address: " << email;

	return 0;
}

Quesiton 7
#include <iostream>

using namespace std;

int main()
{
	string x, y, temp;

	cout << "x: ";
	cin >> x;
	cout << "y: ";
	cin >> y;

	if (y < x)
	{
		temp = x;
		x = y;
		y = temp;
	}

	
	cout << "x: " << x << endl;
	cout << "y: " << y << endl;

	return 0;
}