Before a program is written, the variable required in a program is to be declared with considering the value they may contain.

A declaration consists of a data types, followed by variable name, ending with a semicolon.

int a;
float b;
double c;
char j;


        Initial value can be assigned to variable at the same time when they are declared with in a type declaration.
Ex:- int j=123;
        float i=1.2;


A variable can be assigned some value after its creation.
Ex:- int a;
        float b;

General Structure of C- Program

A C program should be written as.

Header files
        Main ()
                Variable declaration;

Input & Output

Data can be entered in the program by mean of some functions which are already defined in the standard C library.

scanf function :
Data entered by input device is taken by C-library function scanf. The usually used input statement is scanf () function.

General syntax of the scanf :

scanf (control string, arg1, arg2, -----, argn);
where control string refers to a string containing required formatting information & arg1, arg2,---- argn are variable that represent the individual input data values.

Conversion character Meaning
C Data item is character
D Data item is integer
E Floating point value
F Floating point value

Ex :


Ex. scanf (“%d”, &age);

The format string must be a text enclosed in double quotes. It contains the information for interpreting the entire data for connecting it into internal representation in memory.

Writing Output

printf ():-
The usually used output statement is printf (). It is one of the library functions.
Syntax: printf (“format string”, argument list);

Format string may be a collection of escape sequence or/and conversion specification or/and string constant. The format string directs the printf function to display the entire text enclosed within the double quotes without any change.