Introduction to C Language

 

 History of C language.

The C Language was created by Dennis Ritchie at the laboratories in 1972. The UNIX system was developed in C Language between 1977 and 1979. In 1983 the American National Standards Institute (ANSI) to amend and standardized the language. In 1972 and still it is rank 2 on the TIOBE Index and 4 in IEE Spectrum Index. C was firstly developed for the UNIX Operating System. C is also called the mother of modern programing languages.

What are the key features of C programing  that makes it unique?

• Pointer mechanism.
• Functions.
• Extensible.
• Library functions.
• Compiled language.

Applications of C Language.

• Operating Systems.
• Language Compilers.
• Assemblers.
• Databases.
• Utilities.
• Text Editors.

Structure of C language.

• Documentation.
• Preprocessor Section.
• Definition.
• Global Declaration.
• Main () Function.
• Sub Program.
  
  
  

Example;

#include <stdio.h>

int main(){

  printf("Hello World!);

  return 0;

}

C New lines

• New lines are indicated by \ n.
• New line is an escape sequence.

Example;

#include <stdio.h>

int main(){

 printf("Hello World!\n");

printf("I love learning C language.");

return 0;

}

C Comments

• C comments prevent execution when testing.

Single line comments

• Single line comments start with (//).
• For short comments we use single line comments.

Example 1;

#include <stdio.h>

int main(){

// This is a comment

printf("Hello World!");

return 0;

}

Example 2;

#include <stdio.h>

int main(){

printf("Hello World!");// This is a comment.

return 0;

}

Multi-line comments

• Multi-line comments start with /* ends with */.
• For long comments we use multi-line comments.

Example;

#include <stdio.h>

int main(){

/* The code below print  the words Hello World! to the screen , and it is amazing*/

printf("Hello World!");

return 0;

}

C Language Variables

 

 C Variables

• Variables stores data values for temporary period of time.
• C language has different types of variables.

• int - stores integers , such as 120, -110
• float - stores decimals floating point numbers , such as 16.55,-16.55
• char - stores single characters , such as 'a ' , 'B'

Syntax

type variablename = value;

Example 1; 

int Number1 = 20;

Example  2;

// Declare a variable

int Number1;

// Assign a value to the variable

Number = 20;

C Format specifiers

• Format specifiers use together printf() function tell compiler type of data variable storing.
• Place holder is also called the variable value.
• Format specifier is indicated by the character "%".

Example;

#include <stdio.h>

int main(){

  int Number1=15;

  printf("%d", Number);// Output is 20

return 0;

}

• int - Format specifier is "%d"
• char - Format specifier is "%c"
• float - Format specifier is "%f "

Example;

#include <stdio.h>

int main(){

 //Create variables

 int Number = 20;

 float FloatNumber = 10.55;

char Letter = 'A';

// Print variables

printf("%d\n", Number);

printf("%f\n", FloatNumber);

printf("%c\n", Letter);

return 0;

} 

Change Variable Values

Example;

#include <stdio.h>

int main(){

 int Number = 20; // Number is 20

 Number = 10;// Now Number is 10

printf("%d" , Number);

return 0;

}

Example;

#include <stdio.h>

int main(){

 int Number = 20; 

 int OtherNumber = 10;

// Assign the value of OtherNumber (10) to Number

Number = OtherNumber;

// Number is now 10, instead of 20

printf("%d", Number);

return 0;

}

 

C Multiple variables

• To declare more than one variable of the same data type using a comma.

Example;

#include <stdio.h>

int main(){

 int x = 5, y = 6, z = 50;

 printf("%d", x + y + z);

return 0;

}

C Variable Names (Identifiers)

Example;

#include <stdio.h>

int main() {

  // Meaningful variable name

  int minutesPerHour = 60;

  

 // Using letters for variable names are not easy to understand what m actually us

 int  m = 60;

printf("%d\n", minutesPerHour);

printf("%d" , m);

return 0;

}

General  rules for naming variables are ;

• Can contain letters, digits and underscore.
• Must begin  with a letter or underscore.
• Case sensitive such as, variable1, Variable.
• Reserved words can not be used as names such as, int.