3. Basic Structure of C Program
• The C programming language is a
popular and widely used programming
language for creating computer
programs.
• Benefits you gain from learning C:
1) be able to read and write code for a large
number of platforms
2) The jump to the object oriented C++
language becomes much easier.
4. Basic Structure of C Program
• C is what is called a compiled language
• This means that once you write your C
program, you must run it through a C
compiler
• The C program is the human-readable
form, while the executable that comes
out of the compiler is the machine-
readable
• What this means is that to write and run a
C program, you must have access to a C
compiler
6. Basic Structure of C Program
• A C program contains these following
basic structures:
1) Comments
2) The #include Directive (C-library)
3) The main() function
4) Variables and Data type
5) C statement
6) Function Body
7. Basic Structure of C Program
/*This is a basic structure C program*/
#include <stdio.h>
void main ()
{
int miles = 26;
int yards;
float kilometers;
kilometers = 1.609 *(miles+yards/1760.0);
printf(“n A marathon is %f kms”,kilometers);
}
1
2
3
4
5
9. Basic Structure of C Program
1.Comments
• To document programs & improve
readability
• Optional & non-executable statement
• Symbols /* and */ or // indicate the
beginning and the end of the comment
block
10. Basic Structure of C Program
/*A comment may be coded like this*/
//A comment may be coded like this
Note:
1. There is no space between (*) and slash (/)
2. Every /* (begin) must be matched with */ (end)
11. Basic Structure of C Program
2.The #include Directive
• Lines beginning with a pound sign (#) are
directives for the preprocessor
• The preprocessor is a utility program that
performs various modifications to the source
program
• A header file contains the source code that
allows the execution of the program
• Standard input/output header file replaces the
directive in the source code
12. Basic Structure of C Program
• The stdio.h header file enables the program to
perform basic input and output operations
• Allows the program to accept input from the
keyboard and display output on the screen
13. Basic Structure of C Program
#include <stdio.h>
Header File
Note:
1. Lines that start with the # sign are preprocessor
directives
2. The angled-bracket pair <> indicates that the
specified library file is the standard library
directory
14. Basic Structure of C Program
3. The main() function
• The main function is the point by where all
C programs start their execution
• The instructions contained within this
function's definition will always be the first
ones to be executed in any C program
• The word main is followed in the code by a
pair of parentheses (())
• These parentheses may enclose a list of
parameters within them
15. Basic Structure of C Program
• Right after these parentheses we can find the
body of the main function enclosed in braces
{ - Left Braces
} – Right Braces
–What is contained within these braces is
what the function does when it is executed
16. Basic Structure of C Program
Format:
data type function_name (parameters)
{
variable;
C statement;
}
void main ()
{
Statement;
Statement;
…………..;
…………..;
}
Body
17. Basic Structure of C Program
4. Variables and Identifiers
• If your program requests a value from the
user, or if it calculates a value, you will
want to remember it somewhere so you
can use it later. The way your program
remembers things is by using variables.
For example;
int b;
• A variable has a name (in this case, b) and
a type (in this case, int, an integer).
variableIdentifier
18. Basic Structure of C Program
• Each variable needs an identifier that distinguishes
it from the others
• A valid identifier is a sequence of one or more
letters, digits or underline characters _
• Variable identifiers always have to begin with a
letter
• They can also begin with an underline character _
, but this is usually reserved for compiler specific
keywords or external identifiers
• Identifiers cannot match with any reserve keywords
19. Basic Structure of C Program
Very important:
The C language is a "case sensitive" language. That means that
an identifier written in capital letters is not equivalent to
another one with the same name but written in small letters.
20. Basic Structure of C Program
5. Data Types
• The basic fundamental data types in C
21. Basic Structure of C Program
6. Reserved Keywords
• All reserved words appear in
lowercase
• What is the difference between
reserved words and standard
identifiers?
• The standard reserved keywords are;
22. Basic Structure of C Program
Keywords
auto double int struct
break else long switch
case enum register typedef
char extern return union
const float short unsigned
continue for signed void
default goto sizeof volatile
do if static while
23. Basic Structure of C Program
7) Constants
Numeric Constant
• Two types of constants; numeric constant and
symbolic constant
• Numeric constant- actual value assigned to
numeric variable, include integer and floating-
point values
• Integer constant- consists of digits and a unary
sign (+ or -)
• Floating point constant- Is a real number, a
numeric value with a decimal point
24. Basic Structure of C Program
Symbolic Constant
• Purpose is to define symbolic constant
• Symbolic constants are coded in
uppercase letters and retains its value
during the program run
• Normally placed at the beginning of
the program
• e.g: #define VALUE 100
25. Basic Structure of C Program
Non-numeric constants
• Character and string
• Character constant-is a single character
assigned to a character variable
• String constant- is a group of characters
assigned to a string variable
• Character constant = ‘R’ ‘n’ ‘$’
• String constant = “October 5th”
