Structures EE2372 Software Design I Dr. Gerardo Rosiles

Introduction Arrays let you group elements of the same type. In many cases we want to group elements of different types that are seen as belonging to the same entity. Consider the information in your drivers license. It is stored as a “data record” on a computer which can be accessed by an officer when you are stopped for a ticket or something.

Introduction This data record is also known as a data structure in programming parlance. What are the elements of driver’s license structures:

Introduction structure driver license { Name DOB DL # Height Eyes Sex Address Expiration Date Picture }

Introduction A structure allows us to encapsulate this information of a well organized way. Each element of the structure can be further split: structure name { first MI last } structure date { month day year } structure address { number street City State ZIP }

C structures C allows us to create structures that combine different types. You use the struct key word with the following syntax: struct structure_name { type1 identifier1; type2 identifier2; type3 identifier3; etc. } The we can create variables that hold all the information as follows: struct_name var1, var2;

C structures – Examples struct date { int month; int day; int year; }; struct student_data { char name[SIZE]; int age; float grade; }; struct full_name { char first[20]; char MI; char last [30]; }; Note that we have included an array in this structure.

Quick introduction to Strings Strings are a way to group characters into words and sentences using arrays of characters. A quick way to create a string is as follows: char word[20]; word = “Hello”; As long as you use less than 19 characters you are fine. WHY?? We will discuss this in Chapter 10.

Using C structures struct student_data student1, student2; student1.name = “sam”; student1.age = 20; student1.grade = 3.5; printf("name: %s\n",student1.name); printf("age: %d\n",student1.age); printf("grade: %f\n",student1.grade); student2=student1; printf("name: %s\n",student2.name); printf("age: %d\n",student2.age); printf("grade: %f\n",student2.grade); } #include #define SIZE 10 main() { struct student_data { char name[SIZE]; int age; float grade; };

Using C structures To access the elements of a structure we use the “dot” operator. Initialization Accessing for printing Copying structure content struct data student1, student2; student1.name = “sam”; student1.age = 20; student1.grade = 3.5; printf("name: %s\n",student1.name); printf("age: %d\n",student1.age); printf("grade: %f\n",student1.grade); student2=student1; printf("name: %s\n",student2.name); printf("age: %d\n",student2.age); printf("grade: %f\n",student2.grade);

Using C structures There are other ways to initialize structures Initialize at declaration time struct data student1={"sam",20,3.5}; Use scanf for user defined values printf(“Enter student name: “); scanf(“ %s \n”, &student1.name); printf(“Enter student age: “); scanf(“%d \n”, &student1.age); printf(“Enter student grade: “); scanf(“%f \n”, &student1.grade);

Using C structures Individual components of structures can be used in any operation as any variable: arithmetic, logical, relational. if (student1.grade < 1.0) printf(“College of Business \n”); if( student_birthday_passed(student.age) ) student.age = student.age + 1;

Using C structures More interesting use of structures: – Structures containing arrays. We have seen this for the name strings. – Structures containing structures. – Arrays of structures.

Structure containing structures Perhaps the most useful feature of structures. Allows structured implementation of data records. Example 2 struct full_name { char first_name[SIZE]; char last_name[SIZE]; }; struct address { char street[SIZE]; unsigned int zipcode; }; struct position { char title[SIZE]; float salary; }; struct worker { struct full_name name; struct address home_address; char tel[SIZE]; struct position category; };

Arrays of structures Same definition as with arrays struct student_data EE2372_students[30]; We can access each structure through an index and then each element of the structure through the dot operator. EE2372_students[17].name = “Gerardo”; EE2372_students[17].age = 25; EE2372_students[17].grade = 4.0; Example 3

Functions and structures We can pass structures to functions as parameters Functions can return structures Example 5 Are parameters passed by value of by reference.? Let’s modify Example 4.