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(B.V.Patel institute of BMC & IT)

STRUCTURE AND

UNIONS

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Defining a structure

Struct book_bank

{

char title [20];

char author[15];

int pages;

float price;

};

A structure is convenient tool for handling a group of logically related different data items. for ex.customer(address,id,name)

Declare structure variable Struct book_bank { char title [20]; char author[15]; int pages; float price; } book_bank book1;

Accessing structure members The link between member and variable

is establish using dot operator For ex.book1.pages=250; Another method for ex. Strcpy(book1.author,”balagurusamy”); Another method we cal also scanf to values scanf(“%d\n”,&book1.pages);

Structure member initialization Compile time main() { struct student { char name[20]; int marks; }stud; stud. marks={50}; …………… }

Rum time

Scanf (“%d \n ”,&stud. marks);

method of initialize structure Structure can be initialize within main or

outside the main

main() { struct student { char name[20]; int marks; }stud; stud. marks={50}; …………… }

struct student { char name[20]; int marks; }stud; Main() { stud. marks={50);

}

Operations on individual member

If(stud1.number == 111) { float

sum=stud1.marks+stud2.marks; stud2.marks *=0.5; }

Array of structure Struct marks { int sub1; int sub2; int sub3; }marks student main() { Struct marks

student[3]={{45,34,61}, {23,55,67},{44,66,55}}; }

Array initializes members like

student[0].subject1=45; student[0].subject2=34; ………………… student[2].subject3= 55 ;

Arrays within structure Struct marks { int number; float subject[3]; }student[2]; here the member subject contains

three elements subejct[0], subejct[1], subejct[2].

these elements can be accessed using appropriate subscript like student[1].subject[2] refer marks obtain in third subject by second student.

Structure within structure Struct salary { char name; char dept; Struct { int houserent; int da; } allowance;}Employee; Now for refer member we can use

employee.allowance.houserent

union Union item { int m; float x; char c; }code; code.m=379;

union It is like structure but main difference is

in term of storage

1000 1001 1002 1003

C

M

X

ENUM is closely related to the #define preprocessor.

It allows you to define a list of aliases which represent integer numbers. For example if you find yourself coding something like:

#define MON 1 #define TUE 2 #define WED 3 You could use enum as below. enum week { Mon=1, Tue, Wed, Thu, Fri

Sat, Sun} days; or enum boolean { FALSE = 0, TRUE };

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int main() { /* * Define a list of aliases */ enum months {Jan=1, Feb, Mar, Apr,

May, Jun, Jul, Aug, Sep, Oct, Nov, Dec}; enum months month; /* define 'month'

variable of type 'months‘ */ printf("%d\n", month=Sep); /* Assign integer value via an alias * This

will return a 9 */ }

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int main() { /* * Define a list of aliases */ enum days {Jan=31, Feb=28, Mar=31,

Apr=30, May=31, Jun=30, Jul=31, Aug=31, Sep=30, Oct=31, Nov=30, Dec=31};

printf("%d\n", month=Feb); /* Assign integer value via an alias * This will return 28 */

}

It is a program that processes our source program before it is passed to the complier.

The preprocessor offers several features called preprocessor directives. Each of these preprocessor directives begins with # symbol. The directives can be placed anywhere in the program but most often placed at the beginning of program. There are four types of preprocessor directives as follow.

  Macro expansion File inclusion Conditional compilation Miscellaneous directives

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#define PI 3.1415

The above statement is called macro definition or macro. During preprocessing the processor replaces every occurrence of PI in program with 3.1415. It is also called macro templates whereas 3.1415 are called macro expansions

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This preprocessor directive causes one file to be included in another. The preprocessor command for file inclusion looks like this:

#include “filename” and it simply easy causes the entire

contents of filename to be inserted into the source code at that point in the program

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if we want, have the compiler skip over part of a source code by inserting the preprocessing commands #ifdef and #endif, which have the general form:

#ifdef macronamestatement 1;statement 2;statement 3;

#endif  If macroname has been #defined, the

block will be processed as usual; otherwise not

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There are two more preprocessor directives available, though they are not very commonly used. They are:

  #undef #pragma

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