********************************************
#include<iostream.h>
int main()
{
int a, n, t;
float p;
cout <<"enter a, n and t" << endl;
cin >> a >> n >> t;
p = 2/3*(a + n)^t;
cout <<"P is " << p << endl;
}
********************************************
Arrays of characters - strings
------------------------------

write a program which allows the user to enter a 
four (4) letter word. the individual characters making
up the word should be stored in individual elements of
an array. the program should print the entered word forwards
and backwards on the screen.
=============================
#include<iostream.h>
void main(void)
{
	char word[4]; //an array of char
	int i; //index
	cout <<"Enter four letters" << endl;;
	i = 0;
	while (i < 4)
	{
		cin >> word[i];
		i ++;
	}
	//print forwards
	cout <<"\nForwards...";
	i = 0;
	while (i < 4)
	{
		cout << word[i];
		i ++;
	}
	//print backwards
	cout <<"\nBackwards...";
	i = 3;
	while (i >= 0)
	{
		cout << word[i];
		i --;
	}
	cout << endl;
}
===============================

the word string refers to a sequential array of characters such as: the cat sat on the mat

strings are used for messages, words, sentences and so on, any sequence of characters, and are very commonly
found in computer programs. you have already used literal strings in your programs, 
like this: cout <<"Have a nice day";,
why are strings different---: when we store characters in a string(an array of characters) a special character is
used as a sentinel to signal the end of array. this special character is called the null char. it is non_printable
and so can safely be used to signify the_end_of_sting. the code of zero, in order to write it in a program, we use
the syntax: '\o'

we could store the message "hello" like this:
message[o] = 'h';
message[1] = 'e';
message[2] = 'l';
message[3] = 'l';
message[4] = 'o';
message[5] = '\o';

===============================
sample string program

#include<iostream.h>
#include<string.h>
void main(void)
{
	char first_name[20], last_name[40], full_name[70];
	cout <<"enter your first name\n";
	cin >> first_name;
	cout <<"enter your last name\n";
	cin >> last_name;
	strcpy(full_name, last_name);
	strcat(full_name, ",");
	strcat(full_name, first_name);
	int len = strlen(full_name);
	cout <<"your full name is " << full_name << endl;
	cout <<"which contains " << len << " characters" << endl;
}

===============================

char sentace[50];
cin >> sentance;

the cat sat

this problem can be overcome by using the member function getline() to read strings which contain spaces.
ex: 
chat sentence[50];
cin.getline(sentence, 50);

******homework
******--------
1. write a program which manipulates an array of 7 integers according
to the following rules:
* the first element is 47;
* the last element is 65;
* the second element is one more than the last element
* the second to the last element is 13 less than the first element
* the the 4th element is the sum of the first two and the last two elements
* the 3rd and 5th elements are both zero

2. write a function which accepts a string as a parameter and returns the number of vowels in it.
volers are A, E, I, O AND U, and their lower case equivalents.