ALQUDS University Department of Computer Engineering

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1 2013/2014 Programming Fundamentals for Engineers Lab Lab Session # 8 Structures, and Enumeration ALQUDS University Department of Computer Engineering Objective: After completing this lab, the students should be able to: 1. Explain the concept of structures and unions 2. Explain how to declare and initialize a struct 3. Perform operations on structures 4. Perform operation on structures and arrays 5. Perform operation on Structures and functions 6. Understand the idea of enumeration, and use it in meaningful programs. Background: Structure is a derived data type used to represent heterogeneous data items. A structure is an aggregation of components that can be treated as a single variable. The components are called members. For example, an employee can be represented with the following attributes: employee_code (string / integer), employee_name (string), department_code (string), salary (float). Structure Declaration C provides facilities to define structures via a template and to declare a tag to be associated with such structures so that it is not necessary to repeat the definition. struct keyword is used to define structures. Dr. Labib Arafeh, Mr. Yacoub Sabatin, Eng. Allam Abu-Mwais, Eng. Nouraldeen Jibreen 1

2 Syntax for structure: struct tag_name type variable-name, variable-name,... type variable-name, variable-name,... type variable-name, variable-name,... : : type variable-name, variable-name,... Structure-variables can be declared separately by specifying: struct tag_name new-structure-variable When declaring structure variables, a separate instance of structure will be created with the name specified and memory will be allocated for that. Individual members will be given a separate memory location. Structure definition and declaration of structure variables can be combined together. Here, tag name is optional. Note: If tag name is not specified in the declaration, no extra structures can be created. Structure Initialization Structure variables can be initialized at the time of declaration. The format used is quite similar to initializing an array. If the structure variable is declared before the main function in the global declaration section, the member variables are automatically initialized to zero or Null depending on the data type of the member variable. If it is partially initialized, uninitialized members are assigned zero or Null. Accessing the members Members of the structure can be accessed by using the member access operator. (dot). If s is a structure variable with a member named m, then the expression s.m refers to the value of the member m within the structure s. General Form: struct_vble. member-field-name Dr. Labib Arafeh, Mr. Yacoub Sabatin, Eng. Allam Abu-Mwais, Eng. Nouraldeen Jibreen 2

3 Experiment 8.1 Step 1: Try the following code, read in data into these structs, print them out, and record/comment on the results. struct employee int code char name[20] int dept_code float salary struct employee emp1, emp2 Dr. Labib Arafeh, Mr. Yacoub Sabatin, Eng. Allam Abu-Mwais, Eng. Nouraldeen Jibreen 3

4 Step 2: Try these, notice that tag name is optional, and there are different ways to achieve the same thing. struct employee int code char name[20] int dept_code float salary emp1, emp2 Experiment 8.2 Step 1: Show whether the following code is correct or not and determined the value for each member. struct std int enrollnum char name[20] int semester float avg struct std student1=101, Diana, 1, 90.78, student2=102, Yara, 1 Step 2: Trace the following code and identify the errors (if any) struct employee int empno = 101 static char[20] empname = AAAA Dr. Labib Arafeh, Mr. Yacoub Sabatin, Eng. Allam Abu-Mwais, Eng. Nouraldeen Jibreen 4

5 Nested Structure Just as arrays of arrays, structures can contain members that themselves are structures. This can be a powerful method to create complex data types (and/or) structures. Note: As you might expect, member structure must be defined prior to its use. struct date int day int month int year struct employee int code char name[20] struct date doj int dept_code float salary emp1, emp2 In this example, if we want to access the year of joining of an employee of emp1, then we can do so by writing: emp1.doj.year Structures and Arrays A structure can have an array as a member, also we can have array(s) of structures. Example struct stud int rollnum char name[20] int semester int avg struct stud student[50] Dr. Labib Arafeh, Mr. Yacoub Sabatin, Eng. Allam Abu-Mwais, Eng. Nouraldeen Jibreen 5

6 Accessing values: student[1].rollnum student[1].name student[1].semester student[1].avg Structures and Functions Structures can be passed to a function via call by value and call by reference methods. When the structure variable (which is not a pointer) is passed as an argument to a function, it is passed using call by value method. All the members are copied into corresponding formal arguments. But changes will not be reflected back Experiment 8.3 Step 1. Trace the following code for errors and correct them, you would end up with a full program that manipulates structs members. struct emp int empno char empname[10] main( ) void display(struct emp) struct emp emp1 = 101, AAAA display(emp1) void display(struct emp emp2) printf( %d, emp2.empno) printf( %s, emp2.empname) Dr. Labib Arafeh, Mr. Yacoub Sabatin, Eng. Allam Abu-Mwais, Eng. Nouraldeen Jibreen 6

7 Enumeration Enumeration or "enum" for short, is a variable type that can be found in C (and many other programming languages such as C++ and C#). The idea is that instead of using an int to represent a set of values, a type with a restricted set of values in used instead. For example if we use the colors of the rainbow, which are: Red Orange Yellow Green Blue Indigo Violet If enums didn't exist, you might use a #define (in C) or const in C++/C# to specify these values: #define red 1 #define orange 2 : or: const int red=1 The problem with this is that there are many more ints than colors. If violet has the value 7, and the program assigns a value of 15 to a variable then it is clearly a bug but might not be detected as 15 is a valid value for an int. Enums to the Rescue! An enum is a user-defined type consisting of a set of named constants called enumerators. The colors of the rainbow would be mapped like this: enum rainbowcolors red, orange, yellow, green, blue, indigo, violet Now internally, the compiler will use an int to hold these and if no values are supplied, red will be 0, orange is 1 etc. Using enums increase the level of abstraction and lets the programmer think about what the values mean rather than worry about how they are stored and accessed. This reduces the occurrence of bugs. Dr. Labib Arafeh, Mr. Yacoub Sabatin, Eng. Allam Abu-Mwais, Eng. Nouraldeen Jibreen 7

8 Another cool example which demonstrates the level of abstraction resulted from using enums: enum Security_Levels black_ops, top_secret, secret, non_secret // don't forget the semi-colon () int main() Security_Levels my_security_level = top_secret if ( my_security_level == black_ops ) printf("welcome Mister Bond\n") open_safe() open_door() else if ( my_security_level == top_secret ) printf("welcome Q\n") open_door() else if ( my_security_level == secret ) printf("please leave Now\n") else if ( my_security_level == non_secret ) printf("warning, The Police have been Called\n") printf("surrender yourself to them immediately!") call_police() return 0 Dr. Labib Arafeh, Mr. Yacoub Sabatin, Eng. Allam Abu-Mwais, Eng. Nouraldeen Jibreen 8

9 Experiment 8.4 Step 1: Trace the following code, what would be the output? Make your comments. #include <stdio.h> enum week sunday, monday, tuesday, wednesday, thursday, friday, saturday int main() enum week today today=wednesday printf("%d day",today+1) return 0 Step 2: Trace and try the following code, after that, try to change the struct to represent a student, change members, and processes accordingly, then make your comments: 1. /* Al-Quds University 2. Programming Fundamentals for Engineers Lab 3. An example using structs in a C program */ 4. #include <stdio.h> 5. /* User defined types */ 6. enum deptcode sales, personnel, packing, engineering 7. typedef enum deptcode DEPT 8. struct person 9. int age, salary 10. DEPT department 11. char name[12] 12. char address[6][20] typedef struct person EMPLOYEE 15. void read_line(char Str[]) 16. int i = 0 char next 17. while ((next = getchar())!= '\n') 18. Str[i] = next 19. i Str[i] = 0 /* Set the null char at the end */ Dr. Labib Arafeh, Mr. Yacoub Sabatin, Eng. Allam Abu-Mwais, Eng. Nouraldeen Jibreen 9

10 24. void print_employee(employee Emp) 25. int i 26. printf(" %d %d %d\n", Emp.age, Emp.salary, Emp.department) 27. printf("%s\n", Emp.name) 28. for (i = 0 i <= 5 i ++ ) printf("%s\n", Emp.address[i]) int main () 32. EMPLOYEE This_Employee 33. int i 34. scanf("%d",& This_Employee.age) 35. scanf("%d",& This_Employee.salary) 36. scanf("%d\n",& This_Employee.department) 37. read_line(this_employee.name) 38. for (i = 0 i <= 5 i ++ ) read_line(this_employee.address[i]) 39. print_employee(this_employee) 40. return Dr. Labib Arafeh, Mr. Yacoub Sabatin, Eng. Allam Abu-Mwais, Eng. Nouraldeen Jibreen 10

11 Post lab #8 1. What distinguishes an array from a structure? 2. Use structs to define a complex number type, build a set of C functions to add, subtract, multiply them..etc. 3. Consider the following structure, Struct int a int *p *p1 How can the content pointed by member pointer p be accessed via structure variable p1? Research this Dr. Labib Arafeh, Mr. Yacoub Sabatin, Eng. Allam Abu-Mwais, Eng. Nouraldeen Jibreen 11

Lab Session # 5 Arrays. ALQUDS University Department of Computer Engineering

Lab Session # 5 Arrays. ALQUDS University Department of Computer Engineering 2013/2014 Programming Fundamentals for Engineers Lab Lab Session # 5 Arrays ALQUDS University Department of Computer Engineering Objective: After completing this session, the students should be able to: