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C was invented in 1972. It's one of the oldest language to ne used even today. It is one of the most widely used programming language in the world. It has influenced many popular language, especially C++ ( Cpp ).

Simple: - C is a Structure based language i.e. we can divide a big program into multiple parts, which makes it easy to write and understand.

Efficient and Fast:

• C is considered to be "close to the computer," meaning we can program the computer to do precisely what we want. Portable: - Program written in C can be run on different types of machines with little or no modification.

Used for:

• For creating desktop applications.
• For developing games.
• For designing Operating System.
• For designing Compilers.

Working of C

1. Writing Souce code: The first step to write a source code for the desired project. The code is written using a Text Editor.

2. Compiling the source code: The Source code is then converted into equivalent machine instructions, so that the computer can understand it.

3. Checking for Errors: The code is checked for all possible errors.

4. Linking: The code is linked with other files code At the beginning of the code header files means other files are mentioned to link the other code with this script.

5. Checking for Errors: The code is checked for all possible errors once again.

6. Execution: The code is then finally executed to get the desired output.

To display output on screen used printf() built-in Function.

we need to create main function

#include <stdio.h> 

int main() {
  printf("Hello World\n");
  // Code to execute 
  return 0;
}

#include <stdio.h> is header file for input/output files in C, everytime you need to input and output you need to mention the header file at beginning of script.

int stand for integer a datatype for numbers(0 - 9).

main() main function main is name of function and in () we pass parameters(remain blank () will also work).

{} in curly braces contain code to be executed.

printf("Hello World") prinf() is function and Hello World is a string because enclosed in double quotation. Always Use Double Quotes

\n use for new line

; end of the statement

/ Comment / used for Single - Line Comments

/* Beginning of Multi-line Comment

End of Multi-line Comment*/

return 0; return is keyword at end of the function to take the value out of function, make sure returntype and return value are same. 0 is and integer(int). returntype is at start of the function before name of functions int main()

} is end of the function

Output:

Hello World

Running on Linux

1. First install package clang

apt-get install clang

2. compile c file

clang file.c

3. Execute c file

./a.out

To clear the screen

#inlcude <stdlib.h>
...
system("clear");

#include <header file>

returntype functionName(parameters) {
  return 0;
}

Example:

#include <stdio.h>

int main() {
  return 0;
}

Comments help programmers to understand the program code does. Comments are short summary or description about code.

Comments are lgnored by Compiler, Comments are not compiled, write a comment to understand the code how it's code execute.

// Comments you can one line comment, the line will be ignored by compiler, you can also comment the code.

but what if you want to comment more than 15 lines. You can add // at beginning of line not all.

// Comments are here 

/* Begining of 
Multi-line Comments

End of
Multi-line Comments */

Use for multi-line.

prinf() is use for ouput.

printf("Hi");

Display Hi on screen.

scanf() is use for input.

scanf("%d", &var);

take input as number and store in var variable name.

What if you want store something. Variables are like containers or boxes stored values like numbers, string, decimals numbers, etc.

// Variable Initialization 

int main() { 
  int variable_name = value;
return 0;
}

Define dataype, variable_name and value in line.

Example

// Variable Defination 

int main() { 
  int a;
  a = 2;
  return 0;
}

Values are of many types:

• int integers, numbers 0 to 9 are intergers datatype.

• char character, 'A' - 'Z' 'a - b' single letter, character enclosed with single quotation.

• float floating-point number/decimal number with 7 decimal places 0.123

• double decimal number with 15 decimal places 0.123456789012345

int varname = 23;
printf("%d", varname);

first initialise variable then use printf function adding "%d" as digit as datatype. specifying the variable.

char varname = 'A';
printf("use as %c", varname);

Output:

use as A

use as is a string enclosed in double quotation and %c specify the variable use here is %c for character

Computer can take decision on based of input or according to result.

True or False, Yes or No are examples of decisions.

• if
• else

Syntax:

if (condition) {
  printf("condition is TRUE");
}else {
  printf("condition is FALSE")
}

if block execute when condition is True or else block will execute.

Example:

int a = 0;
if (a > 2) {
  printf("a is greater than 2");
}else {
  printf("a is less than 2");
}

Output:

a is less than 2

What if you need to repeat the task/function/...

We use Loops for it.

• for loops
• while loops
• do... while Loops

Syntax:

for (init; condition;  increment/decrement) {
  // Your Task to execute 
}

1. for loops start with for keyword.
2. init This is starting value that will checked and increment in the condition.
3. condition loops repeating itself until the condition is false.
4. increment varaible keep increase until the condition is true.
5. write code inside in {} curly braces.
6. init, condition and increment are separated by ; semicolon.

Example:

for (i = 1; i < 6; i++){
  // Rest of code
  printf("Hello");
}

1. init (i = 1) variable i initial as 1. loops start from 1 and end 5.
2. condition (i < 6) loop will repeat till 5 times at 6 time condition is false so loop ends.
3. increament (i++) value will increase 1 time each loop execute.

Output:

Hello
Hello
Hello
Hello
Hello

Syntax:

// first initialazed the variable
while (condition) {
  // Code to be Execute
}

Example:

int a = 1;
while (a < 6) {
  // Code to be executed
  printf("Hi");
  a++
}

1. firstly initialazed Variable a = 1. loop start from 1 till 5.
2. while keyword for while loop.
3. condition i < 6 means loops will start from 1 and end 5, loops execute 5 times. if a = 0 than loops will run 6 times.
4. write taks in `{}`` curly braces.
5. at last before close curly brace increament variable a++.

Output:

Hi // i = 1
Hi // i = 2
Hi // i = 3
Hi // i = 4
Hi // i = 5

Syntax:

int a = 0; // Initialisation
do {
  // Code 
} while (condition);

Example:

int i = 1;
do {
  printf();
  i = i + 1;
} while (i < 1);

This loop will execute at least one time. condition is false then also loop run 1 time. condition check at last.

Array is variable that contains multiple values but same datatype (numbers/string, etc) and identify by index number. index number start from 0. Arrays value called elements.

Numbers of elements in Arrays can store is called arrays size

Arrays Declaration

datatype arrayname [arraysize];

int array[5];

Arrays Initialization

means giving value to an arrays or assigning value to an array.

array[0] = 5;
array[1] = 6;
array[2] = 7;
array[3] = 8;
array[4] = 8;
array[5] = 9;

One line

int array[5] = {5, 6, 7, 8, 9};

Accessing array by for loop through index.

int array[5] = {1, 2, 3, 4, 5};
for (int i = 0; i < 5; i++) {
  printf("Value at the element %d is %d\n", i, array[i]);
}

Output

Value at the element 0 is: 1 
Value at the element 1 is: 2
Value at the element 2 is: 3
Value at the element 3 is: 4
Value at the element 4 is: 5

Function is group of statements.

Syntax:

returntype functionName (parameters) {
  // Function Body
  return value;
}

returntype : if you want your function to return some values as a result of the task, the datatype of this return value will com here.

void: If your function doesn't return any value, then void is use.

functionName: give function a name.

(parameters): You can pass values to function to perform task. parameters are separated by , comma parameters are optional.

function body write task here enclosed with {} curly braces.

return value;: if you want to return any value you have write return value; at end of function body before enclosed of } closing curly brace. Make sure to datatype of returntype and return value are same

int addition (int num1,int num2) {
  int result;
  result = num1 + num2;
  return result;
}

to call a function, addition function.

int a = 10;
int b = 20;
int c;

c = addition(a,b);
printf("Addition is %d",c);