Basics of C Language 

C Fundamentals

1️. Character Set

C uses a standard set of characters:

• Letters: A–Z, a–z

• Digits: 0–9

• Special Symbols: + - * / = < > ; , { } ( ) [ ] # & % etc.

• Whitespace: Space, Tab, Newline
  
  

2️. Tokens in C

Tokens are the smallest units of a C program. They include:

Token Type Examples

Keywords int, return, if, while, for

Identifiers Variable or function names like age, main

Constants 10, 3.14, 'A', "Hello"

Operators +, -, *, =, ==, &&

Special Symbols ;, {}, (), [], ,

Keywords: - Keywords in C programming are reserved words that have predefined meanings to the C compiler. These words cannot be used as identifiers (such as variable names, function names, or struct names) because they serve specific purposes in the language's syntax . There are total 32 Keywords . 

auto          break          case          char           const          continue          default          do               double

else          enum          extern        float            for               goto                 if                  int                long

register     return          short         signed        sizeof          static               struct           switch           typedef

union       unsigned      void          volatile        while

Identifiers:-

In C programming, identifiers are user-defined names used to uniquely identify various program elements. These elements include variables, functions, arrays, structures, unions, and labels. 

Rules for Identifiers :-

• Identifier names are unique.

• Cannot use a keyword as identifiers.

• Identifier has to begin with a letter or underscore (_).

• It should not contain white space.

• Identifiers can consist of only letters, digits, or underscore.

Constants:-

In C programming, constants are fixed values that cannot be altered or changed during the execution of a program. They are also referred to as literals. Constants can be of various data types, including integer, floating-point, character, and string.  

For Example :- PI = 3.14159  , INITIAL = 'A' etc .

Click here for Operators in C 

Basics of C Language

 Structure of a C Program

Every C program has the following structure:

#include <stdio.h>   // Preprocessor directive

#include <conio.h> 

int main() {         // Main function: entry point

   printf(" Welcome to IT Tech"); // Statements

    getch();        // End of program

}

Basic Syntax Rules 

 Element Description

Statements End with a semicolon ;

Braces {}                                                                           Used to group multiple statements (e.g., in functions, loops)

Comments                                                                               // Single-line, /* Multi-line */

Comments in C :- 

Single line comment : Single-line comments begin with two forward slashes (//). All text from the // to the end of the line is treated as a comment. 

For example :  printf(" Sum = %d",s);  // Display the result of addtion 

Multi line comment :Multi-line comments begin with a forward slash followed by an asterisk (/*) and end with an asterisk followed by a forward slash (*/). Any text between these delimiters, across multiple lines, is treated as a comment .

For example :  printf(" Sum = %d",s);  /* Display the result of addtion 

printf is output function */

#include directive :-

The #include directive in C is a preprocessor command used to incorporate the contents of a specified file, typically a header file, into the current source code file before compilation . Here '#' is  preprocessor directive . Here some examples of the header files . 

• #include<stdio.h> (Standard Input/Output):
  Provides functions for input and output operations, such as printf() for printing to the console and scanf() for reading input.

• #include<stdlib.h> (Standard Library):
  Contains general utility functions, including memory allocation (malloc(), free()), process control (exit()), string conversions (atoi()), and random number generation (rand()).

• #include<string.h> (String Handling):
  Offers functions for manipulating strings, such as copying (strcpy()), concatenating (strcat()), comparing (strcmp()), and finding lengths (strlen()).

• #include<math.h> (Mathematics):
  Includes mathematical functions like sqrt() (square root), sin() (sine), cos() (cosine), pow() (power), and log() (logarithm).

• #include<Conio.h> (Console Input/Output):
  Includes functions like clrscr()  (clearscreen), getch()  (getcharacter).

main() :- Every executable C program must have exactly one main() function, as it dictates where the program's execution flow will begin. In C programming, the main() function serves as the entry point for program execution. 

  Click Here For Input/Output statements 

OR

 Sections of the C Program or Structure of C program 

There are 6 basic sections responsible for the proper execution of a program. Sections are mentioned below:

1. Documentation

2. Preprocessor Section

3. Global Declaration

4. Main() Function

5. Sub Programs

 1. Documentation

This section consists of the description of the program, the name of the program, and the creation date and time of the program. It is specified at the start of the program in the form of comments. Documentation can be represented as:

// description, name of the program, programmer name, date, time etc.

or

/*

   description, name of the program, programmer name, date, time etc.

*/

2. Preprocessor Section

All the header files of the program will be declared in the preprocessor section of the program. Header files help us to access other's improved code into our code. A copy of these multiple files is inserted into our program before the process of compilation. 

Example:

#include<stdio.h>

#include<math.h>

3. Global Declaration

The global declaration section contains global variables, function declaration, and static variables. Variables and functions which are declared in this scope can be used anywhere in the program. 

Example:

int num = 18;

4. Main() Function

Every C program must have a main function. The main() function of the program is written in this section. Operations like declaration and execution are performed inside the curly braces of the main program. The return type of the main() function can be int as well as void too. void() main tells the compiler that the program will not return any value. The int main() tells the compiler that the program will return an integer value.

Example:

void main()

or 

int main()

5. Sub Programs

User-defined functions are called in this section of the program. The control of the program is shifted to the called function whenever they are called from the main or outside the main() function. These are specified as per the requirements of the programmer. 

Example:

int sum(int x, int y)

{

   return x+y;

}