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C- language Lecture 7

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Hatem Abd El-Salam

The document discusses C language structures, unions, and enumerations. It defines structures as collections of variables of different types under a single name. Unions are similar to structures but allow accessing only one member at a time. Enumerations define a user-defined data type consisting of integral constants. Structures and unions can be passed to functions by value or reference, and their members accessed using dot or arrow operators.

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Lecture 7 C Language ENG : HATEM ABD EL-SALAM
• Structure • Unions • Enums Agenda
Structure • Structure is a collection of variables of different types under a single name • If you want to store some information about a person: his/her name, citizenship number and salary. You can easily create different variables name, citNo, salary to store these information separately. • However, in the future, you would want to store information about multiple persons. Now, you'd need to create different variables for each information per person: name1, citNo1, salary1, name2, citNo2, salary2. • You can easily visualize how big and messy the code would look. Also, since no relation between the variables (information) would exist, it's going to be a daunting task. • A better approach will be to have a collection of all related information under a single name Person, and use it for every person. Now, the code looks much cleaner, readable and efficient as well.
Structure (Cont.) • Keyword struct is used for creating a structure. • Note: Don't forget the semicolon }; in the ending line. • We can create the structure for a person as mentioned above as:
Structure (Cont.) Structure variable declaration • For the above structure of a person, variable can be declared as:
Structure (Cont.) Structure variable declaration • Another way of creating a structure variable is:
Structure (Cont.) Structure variable declaration • In both cases, two variables person1, person2 and an array person3 having 20 elements of type struct person are created. • Note: When a structure is defined, it creates a user-defined type but, no storage or memory is allocated.
Structure (Cont.) Accessing members of a structure • There are two types of operators used for accessing members of a structure. 1. Member operator(.) 2. Structure pointer operator(->)
Structure (Cont.) 1- Member operator(.) • Any member of a structure can be accessed as: • Suppose, we want to access salary for variable person2. Then, it can be accessed as:
C- language Lecture 7
Structure (Cont.) 2-Structure pointer operator(->) • Structures can be created and accessed using pointers. A pointer variable of a structure can be created as below: • Here, the pointer variable of type struct name is created.
Structure (Cont.) A structure's member can be accesssed through pointer in two ways: 1. Referencing pointer to another address to access memory 2. Using dynamic memory allocation
Structure (Cont.) 1- Referencing pointer In this example, the pointer variable of type struct person is referenced to the address of person1. Then, only the structure member through pointer can accessed.
Structure (Cont.) 1- Referencing pointer Using -> operator • Structure pointer member can also be accessed using -> operator.
Structure (Cont.) 1- dynamic memory • To access structure member using pointers, memory can be allocated dynamically using malloc() function defined under "stdlib.h" header file.
C- language Lecture 7
Structure (Cont.) • Structures within structures • Structures can be nested within other structures in C programming. • Suppose, you want to access imag_value for num2 structure variable then, following structure member is used.
Structure (Cont.) Passing structures to a function There are mainly two ways to pass structures to a function: 1. Passing by value 2. Passing by reference
Structure (Cont.) Passing by value • A structure variable can be passed to the function as an argument as a normal variable. • If structure is passed by value, changes made to the structure variable inside the function definition does not reflect in the originally passed structure variable.
Structure (Cont.)
Structure (Cont.) Passing by reference • The memory address of a structure variable is passed to function while passing it by reference. • If structure is passed by reference, changes made to the structure variable inside function definition reflects in the originally passed structure variable.
C- language Lecture 7
EXERCISES
Exercises • Calculate Difference Between Two Time Period • Store Information of 10 Students Using Structure
C- language Lecture 7
Unions • Unions are quite similar to structures. Like structures, unions are also derived types. • Defining a union is as easy as replacing the keyword struct with the keyword union.
Unions • Union variables can be created in similar manner as structure variables. OR • In both cases, union variables car1, car2 and union pointer variable car3 of type union car is created.
Unions Accessing members of a union • Again, the member of unions can be accessed in similar manner as structures. • Using pointer.
Unions Passing Union To a Function • Union can be passed in similar manner as structures in C programming.
Unions Difference between union and structure • Though unions are similar to structure in so many ways, the difference between them is crucial to understand • The primary difference can be demonstrated by this example:
C- language Lecture 7
Unions Difference between union and structure • As seen in the above example, there is a difference in memory allocation between union and structure. • The amount of memory required to store a structure variable is the sum of memory size of all members. • But, the memory required to store a union variable is the memory required for the largest element of an union.
Unions • only one of its members can be accessed at a time and all other members will contain garbage values.
C- language Lecture 7
Enumeration • An enumeration is a user-defined data type that consists of integral constants. To define an enumeration, keyword enum is used. • Here, name of the enumeration is flag. • And, const1, const2,...., constN are values of type flag. • By default, const1 is 0, const2 is 1 and so on. You can change default values of enum elements during declaration (if necessary).
Enumeration (Cont.) • When you create an enumerated type, only blueprint for the variable is created. Here's how you can create variables of enum type. • Here, a variable check of type enum boolean is created. • another way to declare same check variable using different syntax
Enumeration (Cont.) • Changing default values of enum.
Enumeration (Cont.) • Example1:
Enumeration (Cont.) • Example2:
Enumeration (Cont.) • Example3:
C- language Lecture 7

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C- language Lecture 7

  • 1. Lecture 7 C Language ENG : HATEM ABD EL-SALAM
  • 3. Structure • Structure is a collection of variables of different types under a single name • If you want to store some information about a person: his/her name, citizenship number and salary. You can easily create different variables name, citNo, salary to store these information separately. • However, in the future, you would want to store information about multiple persons. Now, you'd need to create different variables for each information per person: name1, citNo1, salary1, name2, citNo2, salary2. • You can easily visualize how big and messy the code would look. Also, since no relation between the variables (information) would exist, it's going to be a daunting task. • A better approach will be to have a collection of all related information under a single name Person, and use it for every person. Now, the code looks much cleaner, readable and efficient as well.
  • 4. Structure (Cont.) • Keyword struct is used for creating a structure. • Note: Don't forget the semicolon }; in the ending line. • We can create the structure for a person as mentioned above as:
  • 5. Structure (Cont.) Structure variable declaration • For the above structure of a person, variable can be declared as:
  • 6. Structure (Cont.) Structure variable declaration • Another way of creating a structure variable is:
  • 7. Structure (Cont.) Structure variable declaration • In both cases, two variables person1, person2 and an array person3 having 20 elements of type struct person are created. • Note: When a structure is defined, it creates a user-defined type but, no storage or memory is allocated.
  • 8. Structure (Cont.) Accessing members of a structure • There are two types of operators used for accessing members of a structure. 1. Member operator(.) 2. Structure pointer operator(->)
  • 9. Structure (Cont.) 1- Member operator(.) • Any member of a structure can be accessed as: • Suppose, we want to access salary for variable person2. Then, it can be accessed as:
  • 11. Structure (Cont.) 2-Structure pointer operator(->) • Structures can be created and accessed using pointers. A pointer variable of a structure can be created as below: • Here, the pointer variable of type struct name is created.
  • 12. Structure (Cont.) A structure's member can be accesssed through pointer in two ways: 1. Referencing pointer to another address to access memory 2. Using dynamic memory allocation
  • 13. Structure (Cont.) 1- Referencing pointer In this example, the pointer variable of type struct person is referenced to the address of person1. Then, only the structure member through pointer can accessed.
  • 14. Structure (Cont.) 1- Referencing pointer Using -> operator • Structure pointer member can also be accessed using -> operator.
  • 15. Structure (Cont.) 1- dynamic memory • To access structure member using pointers, memory can be allocated dynamically using malloc() function defined under "stdlib.h" header file.
  • 17. Structure (Cont.) • Structures within structures • Structures can be nested within other structures in C programming. • Suppose, you want to access imag_value for num2 structure variable then, following structure member is used.
  • 18. Structure (Cont.) Passing structures to a function There are mainly two ways to pass structures to a function: 1. Passing by value 2. Passing by reference
  • 19. Structure (Cont.) Passing by value • A structure variable can be passed to the function as an argument as a normal variable. • If structure is passed by value, changes made to the structure variable inside the function definition does not reflect in the originally passed structure variable.
  • 21. Structure (Cont.) Passing by reference • The memory address of a structure variable is passed to function while passing it by reference. • If structure is passed by reference, changes made to the structure variable inside function definition reflects in the originally passed structure variable.
  • 24. Exercises • Calculate Difference Between Two Time Period • Store Information of 10 Students Using Structure
  • 26. Unions • Unions are quite similar to structures. Like structures, unions are also derived types. • Defining a union is as easy as replacing the keyword struct with the keyword union.
  • 27. Unions • Union variables can be created in similar manner as structure variables. OR • In both cases, union variables car1, car2 and union pointer variable car3 of type union car is created.
  • 28. Unions Accessing members of a union • Again, the member of unions can be accessed in similar manner as structures. • Using pointer.
  • 29. Unions Passing Union To a Function • Union can be passed in similar manner as structures in C programming.
  • 30. Unions Difference between union and structure • Though unions are similar to structure in so many ways, the difference between them is crucial to understand • The primary difference can be demonstrated by this example:
  • 32. Unions Difference between union and structure • As seen in the above example, there is a difference in memory allocation between union and structure. • The amount of memory required to store a structure variable is the sum of memory size of all members. • But, the memory required to store a union variable is the memory required for the largest element of an union.
  • 33. Unions • only one of its members can be accessed at a time and all other members will contain garbage values.
  • 35. Enumeration • An enumeration is a user-defined data type that consists of integral constants. To define an enumeration, keyword enum is used. • Here, name of the enumeration is flag. • And, const1, const2,...., constN are values of type flag. • By default, const1 is 0, const2 is 1 and so on. You can change default values of enum elements during declaration (if necessary).
  • 36. Enumeration (Cont.) • When you create an enumerated type, only blueprint for the variable is created. Here's how you can create variables of enum type. • Here, a variable check of type enum boolean is created. • another way to declare same check variable using different syntax
  • 37. Enumeration (Cont.) • Changing default values of enum.