C VAriables

Variables

On UNIX systems all ints are long ints unless specified as short int explicitly.

NOTE: There is NO Boolean type in C -- you should use char, int or (better) unsigned char.

Unsigned can be used with all char and int types.

To declare a variable in C, do:

var_type list variables;

e.g. int i,j,k;

               float x,y,z;

               char ch;

C Program Structure

C Program Structure

A C program basically has the following form:

• Preprocessor Commands
• Type definitions
• Function prototypes -- declare function types and variables passed to function.
• Variables
• Functions

 

We must have a main() function.

A function has the form:

type function_name (parameters)

              {

                             local variables

                             C Statements

               }

If the type definition is omitted C assumes that function returns an integer type. NOTE: This can be a source of problems in a program.

So returning to our first C program:

  /* Sample program */

              main()

                             {

                             printf( ``I Like C \n'' );

                             exit ( 0 );

                             }

NOTE:

• C requires a semicolon at the end of every statement.
• printf is a standard C function -- called from main.
• \n signifies newline. Formatted output -- more later.
• exit() is also a standard function that causes the program to terminate. Strictly speaking it is not needed here as it is the last line of main() and the program will terminate anyway.

Let us look at another printing statement:

printf(``.\n.1\n..2\n...3\n'');

The output of this would be:

              .

              .1

              ..2

              ...3

The C Compilation Model

We will briefly highlight key features of the C Compilation model (Fig. 2.1) here.

                                                                               Source Code

 

  

                                                                               

                The C Compilation Model