C

Fundamental concept of Problem solving
Introduction
Problem solving strategies
Program design & implementation
Introduction to C
Introduction to C
How to open C program code window
Description of C code window
Editing File
Saving and Running a program
The components of C language
Structure of C Program
A sample of C language program
C character set and keywords
C character set and keywords
The C character set
Identifiers
Key words
Data Types
Data Types
Primary Data Type
Secondary Data Type
Variables
Introduction
Rules for constructing variables names
Variable declaration
Assigning values to variables
Scope of variables: Local & Global
Constants
Introduction
Character constants
Integer constants
Real constants
Logical & String constants
C instruction set
Introduction
Type Declaration & Input/Output Instructions
Arithmetic Instructions
Control Instructions
Operators
Introduction
Arithmetic operators
Relational operators
Logical operators
Increment & Decrement operators
Bitwise operators
Conditional & ternary operators
The comma operators
Size of operator
Assignment operator
Type modifier
Expressions
Evaluation of expression
Automatic type conversion
Basic Input/Output
Introduction
Console I/O function
Disc & Port I/O function
Control Structures
Sequence control statements
Decision control & conditional statements
Case control statements
Repitition & loop control statements
Some more statements
Array and String
Introduction of Array
Array Declaration
Array Initialization
Two Dimensional Array
Multi Dimensional Array
String
Function and Recursion
Function Definition
Function Declaration
Function Call
Recursion
Pointers
Introduction
Pointer expression
Pointer & functions
Pointer & Array
Multi Dimensional Arrays & Pointer
Arrays of Pointer
Use of Pointer & functions
Structures
Introduction
Giving values to member
Structure Initialization
Comparison of structure variables
Arrays of structures
Arrays within structures
Structures within structures
Passing structure to function
Union
Introduction
Accessing a union member
Initialization of Union variable
Uses of Union
Dynamic Data Structure
Linked list
Stack
Queue
Data File Handling through C
Introduction
File operation
Opening & closing a data file
Creating a data file
Processing a data file
Unformatted data file
C Preprocessor & Macro
Introduction
Macro substitution directives
File inclusion
Compiler control directive
Command line parameter of C
Command line parameter
Header file
Header file
Use of library functions
Some Useful library functions

Command line parameter of C


Command line parameter

You may have been wondering about the empty parentheses in the first line of the main function, i.e. main().
 
The parentheses may contain special arguments that allow parameters to be passed to main from the operating system.
 
Most versions of C permit two such arguments, which are traditionally called argc and argv, respectively.
 
The first of these, argc, must be an integer variable, while the second, argv, is an array of pointers of characters; i.e., an array of strings.
 
Each string in this array will represent a parameter that is passed to main. The value of argc will indicate the number of parameters passed.
 
Example: The following outline indicates how the arguments argc and argv are defined within main.
 
Vod main(int argc, char *argv[])
{
.....
}
 
The first line can be written without the keyword void, i.e.,
 
main(int argc, char *argv[])
 
A program is normally executed by specifying the name of the program within a menu-driven environment.
 
Some compilers also allow a program to be executed by specifying the name of the program (actually, the name of the file containing the compiled object program) at the operating system level.
 
The program name is then interpreted as an operating system command. Hence, the line in which its appears is generally referred to as a command line.
 
In order to pass one or more parameters to the program when it is executed from the operating system, the parameters must follow the program name on the command line.
 
E.g.: Program-name parameter 1 parameter 2 . . . parameter n
 
The individual items must be separated from one another either by blank spaces or by tabs.
 
Some operating systems permits blank spaces to be included within a parameter provided the entire parameter is enclosed in quotation marks.
 
The program name will be stored as the first item in argv, followed by each of the parameters. Hence, if the program name is followed by n parameters.
 
There will be (n+1) entries in argv, ranging from argv [0] to argv [n]. Moreover, argc will automatically be assigned the value (n+1).
 
Note that the value for argc is not supplied explicitly from the command line.
 
An example program which will be executed from a command line:
 
 
Output of the program
 
 
This program allows an unspecified number of parameters to be entered from the command line.
 
When the program is executed, the Count value for argc and the elements of argv will be displayed as separate lines of output.
 
Sample red white blue
 
then the program will be executed, resulting in the following output.
 
argc =4
argv [0]=sample.exe
argv [1]=red
argv [2]=white
argv [3]=blue
 
The output tells us that four separate items have been entered form the command line.
 
The first is the program name, sample. exe, followed by the three parameters., red. White and blue.
 
Each item is an element in the array argv. (Name that sample.exe is the name of the object file resulting from the compilation of the source code sample. C.)
 
Similarly, if the command line is
 
Sample red "white blue"
 
The resulting output will be
 
argc=3
argv [0]=sample.exe
argv [1]=red
argv [2]=white blue
 
In, this case the string "white blue" will be interpreted as a single parameter, because of the quotation marks.
 
Once the parameters have been entered, they can be utilized within the program in any desired manner.
 
One particularly common application is to specify the names of data files as command line parameter.