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Introduction & History
Ø C is a general-purpose programming language created by Dennis Ritchie at the Bell Laboratories in 1972.
Ø It is a very popular language, despite being old.
Ø C is strongly associated with UNIX, as it was developed to write the UNIX operating system.
Why Learn C?
Ø Many later languages have borrowed syntax/features directly or indirectly from the C language.
Ø Like syntax of Java, PHP, JavaScript, and many other languages are mainly based on the C language.
Ø So, if a person learns C programming first, it will help him to learn any modern programming language as well.
Ø As learning C help to understand a lot of the underlying architecture of the operating system.
Features
Ø The main features of the C language include:
Ø General Purpose and Portable
Ø Low-level Memory Access
Ø Fast Speed
Ø Clean Syntax
Ø These features make the C language suitable for system programming like an operating system or compiler development.
Advantages & Disadvantages
Structure of C Program
Components of a C Program
Header Files Inclusion – Line 1 [#include <stdio.h>]
Ø The first and foremost component is the inclusion of the Header files in a C program.
Ø A header file is a file with extension .h which contains C function declarations and macro definitions to be shared between several source files.
Ø All lines that start with # are processed by a preprocessor which is a program invoked by the compiler.
Ø In the before example, the preprocessor copies the preprocessed code of stdio.h to our file. The .h files are called header files in C.
Ø Some of the C Header files:
Ø stdio.h – Defines core input and output functions
Ø stdlib.h – Defines numeric conversion functions and memory allocation
Ø string.h – Defines string handling functions
Ø math.h – Defines common mathematical functions.
Main Method Declaration – Line 2 [int main()]
Ø The next part of a C program is to declare the main() function.
Ø It is the entry point of a C program and the execution typically begins with the first line of the main().
Ø The empty brackets indicate that the main doesn’t take any parameter.
Ø The int that was written before the main indicates the return type of main().
Ø The value returned by the main indicates the status of program termination.
Body of Main Method – Line 3 to Line 6 [enclosed in {}]
Ø The body of a function in the C program refers to statements that are a part of that function.
Ø It can be anything like manipulations, searching, sorting, printing, etc.
Ø A pair of curly brackets define the body of a function.
Ø All functions must start and end with curly brackets.
Statement – Line 4 [printf(“Hello World”);]
Ø Statements are the instructions given to the compiler.
Ø In C, a statement is always terminated by a semicolon (;).
Ø In this particular case, we use printf() function to instruct the compiler to display “Hello World” text on the screen.
Return Statement – Line 5 [return 0;]
Ø The last part of any C function is the return statement.
Ø The return statement refers to the return values from a function.
Ø This return statement and return value depend upon the return type of the function.
Ø The return statement in our program returns the value from main().
Ø The returned value may be used by an operating system to know the termination status of your program.
Ø The value 0 typically means successful termination.
Compiling Process
Ø The compilation and execution process of C can be divided in to multiple steps:
Ø Preprocessing Using a Preprocessor program to convert C source code in expanded source code. "#include" and "#define" statements will be processed and replaced actually source codes in this step.
Ø Compilation Using a Compiler program to convert C expanded source to assembly source code.
Ø Assembly Using a Assembler program to convert assembly source code to object code.
Ø Linking Using a Linker program to convert object code to executable code. Multiple units of object codes are linked to together in this step.
Ø Loading Using a Loader program to load the executable code into CPU for execution. Compilation
C Preprocessor
Ø C Preprocessor is just a text substitution tool and it instructs the compiler to do required pre-processing before the actual compilation.
Ø All preprocessor commands begin with a hash symbol (#).
Ø It must be the first nonblank character, and for readability, a preprocessor directive should begin in the first column.
Ø We'll refer to the C Preprocessor as CPP.
Ø Preprocessor directives are lines included in a program that begin with the character #, which make them different from a typical source code text.
Ø They are invoked by the compiler to process some programs before compilation.
Ø Preprocessor directives change the text of the source code and the result is a new source code without these directives.
Ø #define SIZE 20 : This directive tells the CPP to replace instances of SIZE with 20. Use #define for constants to increase readability.
Ø #include<stdio.h>: These directives tell the CPP to get stdio.h from System Libraries and add the text to the current source file.
Ø #include “myheder.h”: The next line tells CPP to get myheader.h from the local directory and add the content to the current source file.
Ø #ifndef MESSAGE
#define MESSAGE “Hello”
#endif
Ø It tells the CPP to define MESSAGE only if MESSAGE isn't already defined.
Header Files
Ø A header file is a file with
extension .h which
contains C function declarations and macro definitions to be shared between
several source files.
Ø There are two types of header files:
Ø the files that the programmer writes and
Ø the files that comes with your compiler.
Ø You request to use a header file in your
program by including it with the C preprocessing directive #include, like you have seen inclusion
of stdio.h header
file, which comes along with your compiler.
Library Function
Ø Inbuilt functions in C language.
Ø These inbuilt functions are located in some
common location, and it is known as the library.
Ø All the functions are used to execute a
particular operation.
Ø These library functions are generally
preferred to obtain the predefined output.
Ø Also, the actions of these functions are
present in their header files.
Library Functions in Different Header Files
Advantages of Using C library Functions
Ø The Execution: One of the most significant reasons for utilising the library functions is that these functions are easy-to-use, and have gone through strict testing.
Ø The Functions to Boost the Performance: The standard library functions are very popular. And, that is the reason developers are trying their best to polish them.
Ø Can Save a Lot of Time: The best part is you don’t need to create basic functions, like calculating the square root and more, because we already have these.
Character Set
Ø the character set refers to a set of all the valid characters that we can use in the source program for forming words, expressions, and numbers.
Ø The source character set contains all the characters that we want to use for the source program text.
Ø On the other hand, the execution character set consists of the set of those characters that we might use during the execution of any program.
Ø They include digits, alphabets, special symbols, etc. The C language provides support for about 256 characters.
Types of Characters in C
Alphabets
Ø The C programming language provides support for all the alphabets that we use in the English language.
Ø Thus, in simpler words, a C program would easily support a total of 52 different characters- 26 uppercase and 26 lowercase.
Digits
Ø The C programming language provides the support for all the digits that help in constructing/ supporting the numeric values or expressions in a program.
Ø These range from 0 to 9, and also help in defining an identifier.
Ø Thus, the C language supports a total of 10 digits for constructing the numeric values or expressions in any program.
Special Characters
Ø We use some special characters in the C language for some special purposes, such as logical operations, mathematical operations, checking of conditions, backspaces, white spaces, etc.
Ø We can also use these characters for defining the identifiers in a much better way.
Ø For instance, we use underscores for constructing a longer name for a variable, etc.
Ø The C programming language provides support for the following types of special characters:
White Spaces
Ø The white spaces in the C programming language contain the following:
Ø Blank Spaces
Ø Carriage Return
Ø Tab
Ø New Line
Comments
Ø Comments can be used to explain code, and to make it more readable. It can also be used to prevent execution when testing alternative code.
Ø Comments can be singled-lined or multi-lined.
Ø Single-line Comments
Ø Single-line comments start with two forward slashes (//).
Ø Any text between // and the end of the line is ignored by the compiler (will not be executed).
Ø Example:
Ø // This is a comment
Ø printf("Hello World!");
Ø C Multi-line Comments
Ø Multi-line comments start with /* and ends with */.
Ø Any text between /* and */ will be ignored by the compiler:
Ø Example:
Ø /*
The code below will print the words Hello World!
to the screen, and it is amazing */
Ø printf("Hello World!");
Token and its types
Ø A token is the smallest unit used in a C program.
Ø Each and every punctuation and word that you come across in a C program is token.
Ø A compiler breaks a C program into tokens and then proceeds ahead to the next stages used in the compilation process.
Ø In other words, tokens are the building blocks or the very basic components used in creating any program in the C language.
Ø Different types of token in C:
Ø Identifiers in C
Ø Keywords in C
Ø Operators in C
Ø Strings in C
Ø Special Characters in C
Ø Constant in C
Identifier in C
Ø These are used to name the arrays, functions, structures, variables, etc.
Ø The identifiers are user-defined words in the C language.
Ø These can consist of lowercase letters, uppercase letters, digits, or underscores, but the starting letter should always be either an alphabet or an underscore.
Ø We cannot make use of identifiers in the form of keywords.
Ø Here are the rules that we must follow when constructing the identifiers:
Ø The identifiers must not begin with a numerical digit.
Ø The first character used in an identifier should be either an underscore or an alphabet. After that, any of the characters, underscores, or digits can follow it.
Ø Both- the lowercase and uppercase letters are distinct in an identifier. Thus, we can safely say that an identifier is case-sensitive.
Ø We cannot use an identifier for representing the keywords.
Ø An identifier does not specify blank spaces or commas.
Ø The maximum length of an identifier is 31 characters.
Ø We must write identifiers in such a way that it is not only meaningful- but also easy to read and short.
Keywords in C
Ø We can define the keywords as the reserved or pre-defined words that hold their own importance.
Ø It means that every keyword has a functionality of its own.
Ø Since the keywords are basically predefined words that the compilers use, thus we cannot use them as the names of variables.
Ø If we use the keywords in the form of variable names, it would mean that we assign a different meaning to it- something that isn’t allowed.
Ø The C language provides support for 32 keywords, as mentioned below:
Operators in C
Ø The operators in C are the special symbols that we use for performing various functions.
Ø Operands are those data items on which we apply the operators.
Ø We apply the operators in between various operands.
Ø On the basis of the total number of operands, here is how we classify the operators:
Ø Unary Operator a type of operator that gets applied to one single operand, for example: (--) decrement operator, (++) increment operator, (type)*, sizeof, etc.
Ø Binary Operator types of operators that we apply between two of the operands. Here is a list of all the binary operators that we have in the C language: Relational Operators, Arithmetic Operators, Logical Operators, Shift Operators, Conditional Operators, Bitwise Operators, Misc Operator, Assignment Operator
Ø Ternary Operator Using this operator would require a total of three operands. For instance, we can use the ?: in place of the if-else conditions.
Strings in C
Ø The strings in C always get represented in the form of an array of characters.
Ø We have a ‘\0′ null character at the end of any string- thus, this null character represents the end of that string.
Ø In C language, double quotes enclose the strings, while the characters get enclosed typically within various single characters.
Ø The number of characters in a string decides the size of that string.
Ø Now, there are different ways in which we can describe a string:
Ø char x[9] = “chocolate’’; // Here, the compiler allocates a total of 9 bytes to the ‘x’ array.
Ø char x[] = ‘chocolate’; // Here, the compiler performs allocation of memory during the run time.
Ø char x[9] = {‘c’,’h’,’o’,’c’,’o’,’l’,’a’,’t’,’e’,’\0′}; // Here, we are representing the string in the form of the individual characters that it has.
Special Characters in C
Ø We also use some of the special characters in the C language, and all of them hold a special meaning that we cannot use for any other purpose.
Ø () Simple brackets – We use these during function calling as well as during function declaration. For instance, the function printf() is pre-defined.
Ø [ ] Square brackets – The closing and opening brackets represent the multidimensional and single subscripts.
Ø (,) Comma – We use the comma for separating more than one statement, separating the function parameters used in a function call, and for separating various variables when we print the value of multiple variables using only one printf statement.
Ø { } Curly braces – We use it during the closing as well as opening of any code. We also use the curly braces during the closing and opening of the loops.
Ø (*) Asterisk – We use this symbol for representing the pointers and we also use this symbol as a type of operator for multiplication.
Ø (#) Hash/preprocessor – We use it for the preprocessor directive. This processor basically denotes that the user is utilizing the header file.
Ø (.) Period – We use the period symbol for accessing a member of a union or a structure.
Ø (~) Tilde – We use this special character in the form of a destructor for free memory.
Constant in C
Ø Constant is basically a value of a variable that does not change throughout a program.
Ø The constants remain the same, and we cannot change their value whatsoever.
Ø Here are two of the ways in which we can declare a constant:
Ø By using a #define pre-processor
Ø By using a const keyword
Ø Here is a list of the types of constants that we use in the C language:
Data Types
Ø data types are declarations for variables. This determines the type and size of data associated with variables. For example,
Ø int myVar;
Ø Here, myVar is a variable of int (integer) type. The size of int is 4 bytes.
Ø Basic types
Ø Integers are whole numbers that can have both zero, positive and negative values but no decimal values. For example, 0, -5, 10
Ø We can use int for declaring an integer variable.
Ø int id;
Ø Here, id is a variable of type integer.
Ø You can declare multiple variables at once in C programming. For example,
Ø int id, age;
Ø The size of int is usually 4 bytes (32 bits). And, it can take 232 distinct states from -2147483648 to 2147483647.
Data Type-float and double
Ø float and double are used to hold real numbers.
Ø float salary;
Ø double price;
Ø In C, floating-point numbers can also be represented in exponential. For example,
Ø float normalizationFactor = 22.442e2;
Ø What's the difference between float and double?
Ø The size of float (single precision float data type) is 4 bytes. And the size of double (double precision float data type) is 8 bytes.
Data Type-char &
void
char
Ø Keyword char is used for declaring character type variables. For example,
Ø char test = 'h';
Ø The size of the character variable is 1 byte.
Void
Ø void is an incomplete type. It means "nothing" or "no type". You can think of void as absent.
Ø For example, if a function is not returning anything, its return type should be void.
Ø Note that, you cannot create variables of void type.
Data Type-short &
long
Ø If you need to use a large number, you can use a type specifier long. Here's how:
Ø long a;
Ø long long b;
Ø long double c;
Ø Here variables a and b can store integer values. And, c can store a floating-point number.
Ø If you are sure, only a small integer ([−32,767, +32,767] range) will be used, you can use short.
Ø short d;
Check the size of a
variable-size of
#include
<stdio.h>
int
main() {
short a;
long b;
long long c;
long double d;
printf("size of short = %d
bytes\n", sizeof(a));
printf("size of long = %d bytes\n",
sizeof(b));
printf("size of long long = %d
bytes\n", sizeof(c));
printf("size of long double= %d
bytes\n", sizeof(d));
return 0;
}
Data Type-signed
& unsigned
Ø In C, signed and unsigned are type
modifiers. You can alter the data storage of a data type by using them:
Ø signed
- allows for storage of both
positive and negative numbers
Ø unsigned - allows for storage of only positive
numbers
Ø For example,
Ø // valid codes
Ø unsigned int x = 35;
Ø int y = -35; // signed int
Ø int z = 36;
// signed int
Ø // invalid code: unsigned int cannot hold
negative integers
Ø unsigned int num = -35;
Ø Here, the variables x and num can hold only
zero and positive values because we have used the unsigned modifier.
Ø Considering the size of int is 4 bytes,
variable y can hold values from -231 to 231-1, whereas
variable x can hold values from 0 to 232-1.
Derived data types
Ø Data types that are derived from fundamental data types are derived types.
Ø For example: arrays, pointers, function types, structures, etc.
Ø We will learn about these derived data types in later class.
Escape Sequences
Ø An escape sequence in C language is a sequence of characters that doesn't represent itself when used inside string literal or character.
Ø It is composed of two or more characters starting with backslash \.
Ø For example: \n represents new line.
Ø List of Escape Sequences in C.
Escape Sequence
Example
Output:
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