Lecture 11 C Programming

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Lecture 11C Programming

• Arne Kutzner

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C Structures
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Structure

• A Structure is a container, it can hold a bunch
  of things.
• These things can be of any type.
• Structures are used to organize related data
  (variables) into a nice neat package.

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Example - Student Record

• Student Record
• Name a string
• HW Grades an array of 3 doubles
• Test Grades an array of 2 doubles
• Final Average a double

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Structure Members

• Each thing in a structure is called member.
• Each member has a name, a type and a value.
• Names follow the rules for variable names.
• Types can be any defined type.

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Example Structure Definition

• struct Student
• char name // student name
• double hw3 // homework grades
• double test2 // test grades
• double ave // final average

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Using a struct

• By defining a structure you create a new data
  type.
• Once a struct is defined, you can create
  variables of the new type.
• struct Student stu

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Accessing Members

• You can treat the members of a struct just like
  variables.
• You need to use the member access operator '.'
  (pronounced "dot")
• printf("s", stu.name)
• stu.hw2 82.3
• stu.ave total/100

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Structure Assignment

• You can use structures just like variables
• struct Student s1,s2
• s1.name "Joe Student"
• s2 s1

Copies the entire structure
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Be Careful

• If a member is a pointer, copying means copying
  the pointer (not what is pointed to).

"Joe Student"
name
hw
test
ave
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Pointers to Structures

• Pointers to structures are used often.
• There is another member access operator used with
  pointers -gt
• struct Student sptr
• printf("Name is s", sptr-gtname)
• printf("Ave is d", sptr-gtave)

it looks like a "pointer"!
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Structures and Functions

• Structures are copied if they are passed as
  function argument

void fun(struct Student stu) struct
Student s fun(s)
We copy the structure s !
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Sample Function (won't work!)

• void update_average(struct Student stu)
• double tot0
• for (int i0ilt3i)
• tot stu.hwi
• for (int i0ilt3i)
• tot stu.testi
• stu.ave tot/5

problematical !Why?
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This one works

• void update_average(struct Student stu)
• double tot0
• for (int i0ilt3i)
• tot stu-gthwi
• for (int i0ilt3i)
• tot stu-gttesti
• stu-gtave tot/5

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Structures and malloc

• The malloc function can be used for dynamic
  memory allocation with structures. Example

struct Student student student
malloc(sizeof(struct Student)) student-gtave
0 student-gtname "Kim" free(student)