C Programming Introduction : Tips

1.  Every C Program Should have exactly one main function

2. C Program Execution Always Starts from main.

3. Execution of C Program begins at Opening brace of function and ends at closing

brace of the function

4. Generally all statements in c are written in Lowercase Letters.

5. Uppercase Letters are used for Symbolic names,output strings and messages

6. Every C statement must ends with semicolon

7. All variables must be declared with respective data types before using .

8. C is free form-Language

9. Comments can be inserted anywhere in C Program , but nested comments are not

supported by C .

10. Braces  are Generally Used for the Grouping of statements

Sample C Program :

//C hello world example

#include <stdio.h>

int main()

{

printf("Hello world\n");

return 0;

}

Step By Step Execution Of C Program

Step 1 : Edit

1. This is First Step i.e Creating and Editing Program.

2. First Write C Program using Text Editor , such as [ Borland C/C++ 3.0 , Notpad+

+,Notpad ]

3. Save Program by using [.C] Extension.

4. File Saved with [.C] extension is called “Source Program“.

Step 2 : Compiling

1. Compiling C Program : C Source code with [.C] Extension is given as input to compiler

and compiler convert it into Equivalent Machine Instruction.

2. In Borland C/C++ 3.0 program can be compiled using key [Alt + F9 ].

3. Compiler Checks for errors  . If source code is error-free then Code is converted into

Object File [.Obj ].

Step 3 : Checking Errors

1. During Compilation Compiler will check for error, If compiler finds any error then it

will report it.

2. User have to re-edit the program.

3. After re-editing program , Compiler again check for any error.

4. If program is error-free then program is linked with appropriate libraries.

Step 4 : Linking Libraries

1. Program is linked with included header files.

2. Program is linked with other libraries.

3. This process is executed by Linker.

Step 5 : Error Checking

1. If run time error occurs then “Run-time” errors are reported to user.

2. Again programmer have to review code and check for the solution.

Compiler :

Compiler takes high level human readable program as input and convert it into the lower level

code.This conversion takes place using different phases.First phase of compiler is lexical

analysis.

Must Read : [What is Compiler ?]

Different phases of compilers :

1. Analysis Phase

2. Synthesis Phase

1.Analysis Phase :

Lexical analysis

Syntax analysis

Semantic analysis

Lexical Analysis Phase :

Task of Lexical Analysis is to read the input characters and produce as output a sequence of

tokens that the parser uses for syntax analysis.

1. Lexical Analyzer is First Phase Of Compiler.

2. Input to Lexical Analyzer is “Source Code“

3. Lexical Analysis Identifies Different Lexical Units in a Source Code.

4. Different Lexical Classes or Tokens or Lexemes

o Identifiers

o Constants

o Keywords

o Operators

5. Example : sum = num1 + num2 ;

So Lexical Analyzer Will Produce following Symbol Table –

Token Type

sum Identifier

= Operator

num1 Identifier

+ Operator

num2 Identifier

; Seperator

6. Lexical Analyzer is also called “Linear Phase” or “Linear Analysis” or “Scanning“

7. Individual Token is also Called Lexeme

8. Lexical Analyzer’s Output is given to Syntax Analysis.

Analysis Phase : 2nd Phase of Compiler (Syntax Analysis)

During the first Scanning phase i.e Lexical Analysis Phase of the compiler , symbol table is

created by the compiler which contain the list of leximes or tokens.

Syntax Analysis :

1. It is Second Phase Of Compiler after Lexical Analyzer

2. It is also Called as Hierarchical Analysis or Parsing.

3. It Groups Tokens of source Program into Grammatical Production

4. In Short Syntax Analysis Generates Parse Tree

Parse Tree Generation :

sum = num1 + num2

Now Consider above C Programming statement. In this statement we Syntax Analyzer will

create a parse tree from the tokens.

[box]Syntax Analyzer will check only Syntax not the meaning of Statement[/box]

Explanation : Syntax Analysis

We know , Addition operator plus (‘+’) operates on two Operands

Syntax analyzer will just check whether plus operator has two operands or not . It does

not checks the type of operands.

Suppose One of the Operand is String and other is Integer then it does not throw error as

it only checks whether there are two operands associated with ‘+’ or not .

So this Phase is also called Hierarchical Analysis as it generates Parse Tree

Representation of the Tokens generated by Lexical Analyzer

Syntax analyzer will just create parse tree. Semantic Analyzer will check actual meaning of the

statement parsed in parse tree. Semantic analysis can compare information in one part of a

parse tree to that in another part (e.g., compare reference to variable agrees with its

declaration, or that parameters to a function call match the function definition).

Semantic Analysis is used for the following –

1. Maintaining the Symbol Table  for each block.

2. Check Source Program for Semantic Errors.

3. Collect Type Information  for Code Generation.

4. Reporting compile-time errors  in the code (except syntactic errors, which are caught

by syntactic analysis)

5. Generating the object code  (e.g., assembler or intermediate code)

Now In the Semantic Analysis Compiler Will Check –

1. Data Type of First Operand

2. Data Type of Second Operand

3. Check Whether + is Binary or Unary.

4. Check for Number of Operands Supplied to Operator Depending on Type of Operator

(Unary | Binary | Ternary)

What is Interpreter ?

1. Interpreter Takes Single instruction as input .

2. No Intermediate Object Code is Generated

3. Conditional Control Statements are Executes slower

4. Memory Requirement is Less

5. Every time higher level program is converted into lower level program

6. Errors are displayed for   every instruction  interpreted (if any)

7. The interpreter can immediately execute high-level programs, thus interpreters are

sometimes used during the development of a program, when a programmer wants to

add small sections at a time and test them quickly.

8. In addition, interpreters are often used in education because they allow students to

program interactively.

Examples of Programming Languages Using Interpreter :

Lisp

(defun convert ()

(format t "Enter Fahrenheit ")

(LET (fahr)

(SETQ fahr (read fahr))

(APPEND '(celsisus is) (*(- fahr 32)(/ 5 9)) )

)

)

BASIC

CLS

INPUT "Enter your name: ", Name$

IF Name$="Mike" THEN

PRINT "Go Away!"

ELSE

PRINT "Hello, "; Name$; ". How are you today?"

END IF

External Reference Links : Advantages and Disadvantages of Interpreter |Interpreter

Difference between Compiler and Interpreter

No

Compiler Interpreter

1Compiler Takes Entire program as input

Interpreter Takes Single instruction as input .

2Intermediate Object Code isGenerated

No Intermediate Object Code isGenerated

3Conditional Control Statements are Executes faster

Conditional Control Statements are Executes slower

4Memory Requirement : More(Since Object Code is Generated)

Memory Requirement is Less

5Program need not be compiledevery time

Every time higher level program is converted into lower level program

6Errors are displayed after entire program is checked

Errors are displayed for every instruction interpreted (if any)

7 Example : C Compiler Example : BASIC

Explanation : Compiler Vs Interpreter

Just understand the concept of the compiler and interpreter –

1. We give complete program as input to the compiler. Our program is in the human

readable format.

2. Human readable format undergoes many passes and phases of compilerand finally it is

converted into the machine readable format.

3. However interpreter takes single line of code as input at a time and execute that line. It

will terminate the execution of the code as soon as it finds the error.

4. Memory requirement is less in Case of interpreter because no object code is created in

case of interpreter.

Following video will say much more about compiler –

Difference Between Source Code and Object Code

Source Code :

1. Source Code is In the form of Text.

2. Source Code is Human Readable.

3. Source Code is Generated by Human.

4. Source Code is Input Given to Compiler.

Object Code :

1. Object Code is in the form of Binary Numbers.

2. Object Code is in Machine Readable.

3. Object Code is Generated by Compiler.

4. Object code is Output of Compiler.

Also See : Compile Vs Interpreter

Tips for New Programmers 1 : About Simple Program 

1. Include following header file in order to print simply “Hello”

#include<stdio.h>

2. Don’t forgot to write main function.

3. Separate line  for each header file .

4. Each Statement is terminated by Semicolon (;) .

5. Main function starts with opening parenthesis (” { “) and ends with closing parenthesis (”

} “) .

6. Simple Hello Word Program :

#include<stdio.h>

main()

{

printf("Hello World");

}

Tips For Writing Readable And Eye Catching C Program

Tip 1 : Use Stylish Comment to Specify Title Of Program !!

/*********************************************

* Title : Your Title

* Date : DD/MM/YYYY

* Program By : Your Name *********************************************/

Or

/**

* Title : Your Title

* Date : DD/MM/YYYY

* Program By : Your Name

**/

Tip 2 : One Should Use Horizontal Rulers To Differentiate Different Modules

#include< stdio.h>

#include< conio.h>

//----------------------------------------

int add(int,int);

int sub(int,int);

int div(int,int);

//----------------------------------------

void main()

{

............................

}

//----------------------------------------

int add(int a,int b)

{

.....................

}

1. Horizontal Rules Differentiate Source Code into Three Parts –

o Header File Section

o Prototype Declaration Section

o Main Function

2. Horizontal Rule makes Program more Readable

Tip 3 : Must Specify Function Description Before Writing Function Definition.

/*-----------------------------------------------

Search Function : Used to Search Element

-----------------------------------------------*/

int search()

{

.....

.....

.....

}

Tip 4 : Use Proper Indentation [i.e Space]

if(condition)

{

for(i=0;i< n;i++)

{

Statement 1;

Statement 2;

while(i<5)

{

Statement 3;

Statement 4;

Statement 5;

}

}

}

1. One can Understand Program if Proper Indentations are Provided.

2. In Above Program one can Easily Understand Statements Under if,for,while.

Tip 5 : Provide Comment After Nested Closing Braces.

if(condition)

{

for(i=0;i< n;i++)

{

Statement 1;

Statement 2;

while(i<5)

{

Statement 3;

Statement 4;

Statement 5;

} //end of while

}//end of for

}//end of if

1. If You Look at last Three Lines , At First Glance we are unable to Distinguish

Corresponding Closing Brace.

2. So Short but Sweet Comment Can be used to Avoid Your Confusion