CSci 160 Lecture 42

1. CSci 160Lecture 42 Martin van Bommel

2. Structure vs Array • Array - data is • ordered - index number • homogeneous - elements have same type • used for lists or collections • Structure - data is • unordered • heterogeneous • used for real-world objects

3. Structures (Records) • Example: Student • Id Number • Name • Year, Program, Major, etc. Id Name Year Program Major 20050123 John Smith 1 B.Sc. CS • Fields of structure

4. Records in C (Structs) • To create a record, you • Define structure type - field names and types • Declare variables of new type typedef struct { long int id; char name[NameSize]; int year; char program[PSize], major[MSize]; } student_t; student_t student;

5. Record Selection • Once you declare variable student_t student; can refer to it as a whole by name • However, can refer to individual fields student.name • Read it as “student dot name” • Referred to as “component selection”

6. Initializing Records • Can assign components values student.id = 20050123; strcpy(student.name,”John Smith”); student.year = 1; • Or can initialize during declaration student_t student = { 20050123, ”John Smith”, 1, ”B.Sc.”, ”CS” };

7. Simple Records • E.g. A simple point with x and y coordinates typedef struct { double x, y; } point_t; • Can do assignment with structures point1 = point2; • Equivalent to point1.x = point2.x; point1.y = point2.y;

8. Records in Functions • To make a point point_t CreatePoint(double x, double y) { point_t p; p.x = x; p.y = y; return (p); } origin = CreatePoint(0, 0);

9. Records as Arguments double Distance(point_t p1, point_t p2) { int dx, dy; dx = p1.x - p2.x; dy = p1.y - p2.y; return sqrt(dx * dx + dy * dy); }