C notes from scratch to advance | Variable , Constants and Keywords in C | #C

Variables

A variable is a container which stores a ‘value.’

Let me explain this with an example : In the kitchen, we have containers storing rice, dal, sugar, etc.

Similar to that variable in C stores the value of a constant. That value may be different as in kitchen dal , rice and all here we may have Int , Double , String and Float , etc. We will definitely know these all in brief.

Example: 

Rules for naming variables in c:

1. The first character must be an alphabet or underscore( _ ).

2. No commas or blanks are allowed.

3. No special symbol other than underscore is allowed

4. Variable names are case sensitive ( ie: rAm and ram are two different variable )

Definitely we can use a , b , c , d or any random and meaningless things as a name. But I will recommend you to use and create meaningful variables names in our programs. This enhances readability of our programs.

Constants

An entity whose value doesn’t change is called a constant.

or

A data or value which doesn’t change during a whole program are called a Constants.

Types of constant

Primarily there are three types of constant :

Keywords

These are reserved words whose meaning is already known to the compiler.

or

Any reserved words for C are called Keywords.

There are 32 keywords available in C :

Our first C program : 

#include<stdio.h>

int main() {

printf(“Hello, I am learning C with Harry”);
return 0;

}

The basic structure of a C program 

All C programs have to follow a basic structure called syntax.

As we have rules and regulations in every field either its traffic laws or tax rules. Simply their are some set of rules in C or in simple word we have a defined rules for C program called “Syntax“.

Example : A C program starts with the main function and executes instructions presents inside it. Each instruction terminated with a semicolon(;)

• There are some basic rules which are applicable to all the C programs:
  • Every program’s execution starts from the main function.
  • All the statements are terminated with a semi-colon.
  • Instructions are case-sensitive.
  • Instructions are executed in the same order in which they are written.

Comments 

Comments are used to clarify something about the program in plain language. It is a way for us to add notes to our program. There are two types of comments in c:

• Single line comment:
  • //This is a single-line comment.
• Multi-line comment :
  • • /*This is multi-line comment
    •     This is multi-line comment
    •     This is multi-line comment
    •     This is multi-line comment
    •     This is multi-line comment*/

Comments in a C program are not executed and ignored. Compiler simply skips the comments and move forward.

Compilation and execution

A compiler is a computer program that converts a C program into machine language so that it can be easily understood by the computer.

A program is written in plain text. This plain text is a combination of instructions in a particular sequence. The compiler performs some basic checks and finally converts the program into an executable.

Library functions

C language has a lot of valuable library functions which is used to carry out a certain task; for instance, printf function is used to print values on the screen.

printf(“This is %d”,i);

// %d for integers

// %f for real values

// %c for characters

Types of variables

Receiving input from the user

In order to take input from the user and assign it to a variable, we use scanf function.

The syntax for using scanf:

• scanf(“%d”,&i); // [This & is important]

& is the “address of” operator, and it means that the supplied value should be copied to the address which is indicated by variable i.