Structure Basic Idea Ordinary variables can hold one

Structure

Basic Idea • Ordinary variables can hold one piece of information and arrays can hold a number of pieces of information of the same data type. • These two data types can handle a great variety of situations. • But quite often we deal with entities that are collection of dissimilar data types. • For example, suppose you want to store data about a book. You might want to store its name (a string), its price (a float) and number of pages in it (an int). • If data about say 3 such books is to be stored, then we can follow two approaches: • (a) Construct individual arrays, one for storing names, storing prices and still another for storing number of pages. • (b) Use a structure variable.

Introduction • A structure is a user defined data type which keeps variables of different data types under a single name, unlike array which keeps only single data type values.

Cont… • The program becomes more difficult to handle as the number of items relating to the book go on increasing.

Defining a Structure

Memory for Structure • Memory is allocated to structure during creation of variable of structure not during declaration of structure. • Continuous memory is allocated to structure starts from first element of structure • Ex. • struct detail{ int a; char b; int c[10]; }d 1; • Memory Map;

typedef : An example typedef struct{ float real; float imag; } _COMPLEX; _ COMPLEX a, b, c; Syntax: typedef existing_name new_name Example: typedef unsigned int uint; uint a, b; //a, b are of type unsigned int

Example typedef struct{ float real; float imag; } _COMPLEX; void swap (_COMPLEX a, _COMPLEX b) { _COMPLEX tmp; tmp = a; a = b; b = tmp; } void print (_COMPLEX a) { printf("(%f, %f) n", a. real, a. imag); } void main() { _COMPLEX x={4. 0, 5. 0}, y={10. 0, 15. 0}; print(x); print(y); swap(x, y); print(x); print(y); }

Union • Union is user defined data type used to store data of dissimilar types under unique variable name at single memory location. • Syntax of union is similar to structure. • The major difference between structure and union is storage. In structures, each member has its own storage location, whereas all the members of union use the same location. • It can handle only one member at a time. • Union holds value for one data type which requires larger storage among their members.

Union Example #include <stdio. h> union Engg { int id; char name[20]; }Eg; void main() { printf("Enter developer id : "); scanf("%d", &Eg. id); printf("n Enter developer name : "); scanf("%s", Eg. name); printf("n Developer ID : %d", Eg. id); //Garbage Value printf("n Developed By : %s", Eg. name); }

Enum • Enum stands for enumerated data type. • It is user defined data type whose elements are treated as constant. • The enumerator names are usually identifiers that behave as constants in the • language. • First Element of enumerator starts with 0, second element 1, third element 2 and • so on. We can also change the value of elements to our desired choice.

Enum Example #include <stdio. h> enum {sun, mon, tue, wed, thu, fri, sat}; enum {f, t}; enum {zero=1, one, two=5, three}; void main(){ int i; for(i=sun; i<=sat; i++) printf("Code for day is : %d n", i); if(t==1) printf("Enum is Awesome n"); printf("%d ", zero); printf("%d ", one); printf("%d ", two); printf("%d ", three); }

Program for atoi() int my. Atoi(char *str) { int res = 0; // Initialize result for (int i = 0; str[i] != ''; ++i) res = res*10 + str[i] - '0'; return res; // return result. } int main() { char str[] = "9789"; int val = my. Atoi(str); printf ("%d ", val); return 0; } Output: 9789