• The main() function.
• General structure of a C program.
• The semicolon.
• Declaration Statements.
• Assignment Statements.
• Function Statements.
• Control Statements.
• Null statements.

C program

#include

main()

function a()

function b()

#include

main()

{

int num;

num=1;

printf("%d is my number. \n",num);

}

For the above example,

#include is a preprocessor instruction.

int num; is a declaration statement.

Num = 1; is an assignment statement.

printf("%d is my number. \n",num); is a function statement.

the semicolon (;) at the end of a line identifies the line as a C statement or instruction.

Note : the semicolon is part of the statement, not a separator between statements as it is in Pascal.

Declaration statements are used to declare any variables that are to be used in the program.

all variables in a C program must be declared before they are used.

The declaration of variabhle in C has the following general form:

type variahble;

for example,

int num;

the above statement declares a variable called num of integer data type.

The reserved word int is one of the basic C data types.

Reserved words or keywords are specific words used to express a language; they may not be used for any other purpose.

All reserverd words or keywords in C must be in lowercase.

Variable name / identifier choice

use meaningful names

the maximum number of characters for a variable name is compiler dependant

variable names can consist of

letters

digits

the underscore (_) which is treated as a character.

Example:

Valid Names Invalid Names

average $Zoom[**

cow1 1cow

Big_Number Big-Number

_kcab don’t

C language is case sensitive; that is upper and lowercase letters are distinct.

For example the variable names num, Num, and NUM each refer to a different variable.

Assignment statement

the assignment statement is one of the most basic operations to give a variable a value.

For example:

num=1;

means "give the variable num the value of 1".

The assignment statement, like the declaration statement, is completed with a semicolon.

The assignment statement’s general form:

identifier = expression;

the = is called the assignment operator, and C has more than one assignment operator.

• Other assignment operator are:
• += -= *= /= %= <<= >>= &= |= ^=
• Function statements

#include

main()

{

printf("Hello Universe! \n");

printf("Welcome to C language. \n");

}

the statements in the above program uses a standard C function called printf().

Function statements are statements that calls other functions.

The parantheses () after a function name makes it a function statement.

the items enclosed in the parantheses are information passed from the main() function to the function called.

Such information is called the argument(s) or parameter(s) of a function.

These type of statements provide program "flow" control.

There are three forms of program flow control:

executing a series of statements

using a test or condition to decide between alternative actions.

repeating a sequence of statements until some condition is met.

Null statement

essentially does nothing.

Example:

;