hi friends!!!
c/c++ the basics of any one to be called as a software engineer....hmmm of course you might have known all these things..but yet you need to in much more detail..... there are lot more things in C/C++ which can be known only through practice....so common friends...lets start with an intro program....(:P)
#includeLet's look at the elements of the program. The #include is a "preprocessor" directive that tells the compiler to put code from the header called iostream into our program before actually creating the executable. By including header files, you an gain access to many different functions. For example, the cout function requires iostream. Following the include is the statement, "using namespace std;". This line tells the compiler to use a group of functions that are part of the standard library (std). By including this line at the top of a file, you allow the program to use functions such as cout. The semicolon is part of the syntax of C and C++. It tells the compiler that you're at the end of a command. You will see later that the semicolon is used to end most commands in C++.
using namespace std;
int main()
{
cout<<"HEY, you, I'm alive! Oh, and Hello World!\n"; cin.get(); }
The next imporant line is int main(). This line tells the compiler that there is a function named main, and that the function returns an integer, hence int. The "curly braces" ({ and }) signal the beginning and end of functions and other code blocks. If you have programmed in Pascal, you will know them as BEGIN and END. Even if you haven't programmed in Pascal, this is a good way to think about their meaning.
The next line of the program may seem strange. If you have programmed in another language, you might expect that print would be the function used to display text. In C++, however, the cout object is used to display text. It uses the << style="text-align: left;">
#include
using namespace std;
int main()
{
cout<<"HEY, you, I'm alive! Oh, and Hello World!\n"; cin.get(); return 1; } The final brace closes off the function. You should try compiling this program and running it. You can cut and paste the code into a file, save it as a .cpp (or whatever extension your compiler requires) file. If you are using a command-line compiler, such as Borland C++ 5.5, you should read the compiler instructions for information on how to compile. Otherwise compiling and running should be as simple as clicking a button with your mouse. You might start playing around with the cout function and get used to writing C++. Comments are critical for all but the most trivial programs and this tutorial will often use them to explain sections of code. When you tell the compiler a section of text is a comment, it will ignore it when running the code, allowing you to use any text you want to describe the real code. To create a comment use either //, which tells the compiler that the rest of the line is a comment, or /* and then */ to block off everything between as a comment. Certain compiler environments will change the color of a commented area, but some will not. Be certain not to accidentally comment out code (that is, to tell the compiler part of your code is a comment) you need for the program. When you are learning to program, it is useful to be able to comment out sections of code in order to see how the output is affected. So far you should be able to write a simple program to display information typed in by you, the programmer and to describe your program with comments. That's great, but what about interacting with your user? Fortunately, it is also possible for your program to accept input. The function you use is known as cin, and is followed by the insertion operator >>.
Of course, before you try to receive input, you must have a place to store
that input. In programming, input and data are stored in variables. There are
several different types of variables; when you tell the compiler you are
declaring a variable, you must include the data type along with the name of
the variable. Several basic types include char, int, and float.
A variable of type char stores a single character, variables of type int store
integers (numbers without decimal places), and variables of type float store
numbers with decimal places. Each of these variable types - char, int, and
float - is each a keyword that you use when you declare a variable.
Sometimes it can be confusing to have multiple variable types when it seems
like some variable types are redundant. Using the right variable size can be
important for making your code readable and for efficiency--some variables
require more memory than others. For now, suffice it to say that the
different variable types will almost all be used!
To declare a variable you use the syntax type . It is permissible
to declare multiple variables of the same type on the same line; each one
should be separated by a comma. The declaration of a variable or set of
variables should be followed by a semicolon (Note that this is the same
procedure used when you call a function). If you attempt to use an undefined
variable, your program will not run, and you will receive an error message
informing you that you have made a mistake. Don't forget that variables, just
like keywords, are case-sensitive, so it's best to use a consistent
capitalization scheme to avoid these errors.
Here are some variable declaration examples:
int x;
int a, b, c, d;
char letter;
float the_float;
While you can have multiple variables of the same type, you cannot have
multiple variables with the same name. Moreover, you cannot have
variables and functions with the same name.
Here is a sample program demonstrating the use a a variable:
#include
using namespace std;
int main()
{
int thisisanumber;
cout<<"Please enter a number: "; cin>> thisisanumber;
cin.ignore();
cout<<"You entered: "<<>> reads a value
into thisisanumber; the user must press enter before the number is read by the
program. cin.ignore() is another function that reads and discards a character.
Remember that when you type intput into a program, it takes the enter key too.
We don't need this, so we throw it away. Keep in mind that the variable was
declared an integer; if the user attempts to type in a decimal number, it will
be truncated (that is, the decimal component of the number will be ignored).
Try typing in a sequence of characters or a decimal number when you run the
example program; the response will vary from input to input, but in no case is
it particularly pretty. Notice that when printing out a variable quotation
marks are not used. Were there quotation marks, the output would be "You
Entered: thisisanumber." The lack of quotation marks informs the compiler that
there is a variable, and therefore that the program should check the value of
the variable in order to replace the variable name with the variable when
executing the output function. Do not be confused by the inclusion of two
separate insertion operators on one line. Including multiple insertion
operators on one line is perfectly acceptable and all of the output will
go to the same place. In fact, you must separate string literals (strings
enclosed in quotation marks) and variables by giving each its own insertion
operators (<<). Trying to put two variables together with only one <<>, <. The * multiplies, the - subtracts, and the + adds. It is of course important to realize that to modify the value of a variable inside the program it is rather important to use the equal sign. In some languages, the equal sign compares the value of the left and right values, but in C++ == is used for that task. The equal sign is still extremely useful. It sets the left input to the equal sign, which must be one, and only one, variable equal to the value on the right side of the equal sign. The operators that perform mathematical functions should be used on the right side of an equal sign in order to assign the result to a variable on the left side. Here are a few examples: a = 4 * 6; // (Note use of comments and of semicolon) a is 24 a = a + 5; // a equals the original value of a with five added to it a == 5 // Does NOT assign five to a. Rather, it checks to see if a equals 5. The other form of equal, ==, is not a way to assign a value to a variable. Rather, it checks to see if the variables are equal. It is useful in other areas of C++; for example, you will often use == in such constructions as conditional statements and loops. You can probably guess how <> function. They are greater than and
less than operators.
For example:
a <> 5 // Checks to see if a is greater than five
a == 5 // Checks to see if a equals five, for good measure
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