240-222 CPT: Types/6 1

240-222 Computer Programming Techniques240-222 Computer Programming TechniquesSemester 1, 1998Semester 1, 1998

Objective of these slides:– to look at how new types can be created

6. User-defined Types

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OverviewOverview

1. Enumeration Types

2. typedef

3. Structures (struct)

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1. Enumeration Types Sec. 10.111. Enumeration Types Sec. 10.11

1.1. Declaring Enumeration Types and Variables

1.2. Using Enumeration Type Variables

1.3. Initialisation

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1.1. Declaring Enumeration Types 1.1. Declaring Enumeration Types and Variablesand Variables

An enumeration type is a finite set. enum day {SUN, MON, TUE, WED, THU,

FRI, SAT};

Declare variables of the enum day type:enum day d1, d2;

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1.2. Using Enumeration Type 1.2. Using Enumeration Type VariablesVariables

Assignment can only use enumerators:d1 = FRI;d2 = MON;

Testing:if (d1 == d2) . . . /* do something */

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1.3. Initialisation1.3. Initialisation

enum suit {CLUBS = 1, DIAMONDS, HEARTS, SPADES};

enum suit a, b,c;

Or:

enum suit {CLUBS = 1, DIAMONDS, HEARTS, SPADES} a, b, c;

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2. typedef Sec. 10.62. typedef Sec. 10.6

2.1. Using typedef Types

2.2. What is Tomorrow?

2.3. Advanced typedef Use

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2.1. Using Typedef Types2.1. Using Typedef Types

typedef is for defining new type names:

typedef int age;/* typedef <current type> <new type>; */

Declare 3 variables:age s, t, u;

Use:s = 18;

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2.2. What is Tomorrow?2.2. What is Tomorrow?

/* Manipulating a day type */#include <stdio.h>

enum day {SUN, MON, TUE, WED, THU, FRI, SAT};

typedef enum day Day;

Day get_next_day(Day d);/* enum day get_next_day(enum day d); */

:

continued

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int main(){ Day d1 = MON; : d1 = get_next_day(d1); : return 0;}

continued

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Day get_next_day(Day d){ Day next_day;

switch (d) { case SUN: next_day = MON; break; case MON: next_day = TUE; break; : /* a case for each day */ : case SAT: next_day = SUN; break; } return next_day;}

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Or:Or:

Day get_next_day(Day d)/* Compute the next day with a cast */{ return ( (Day) (( (int) d + 1)% 7 ));}

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2.3. Advanced Typedef Use2.3. Advanced Typedef Use

typedef float vector[10];vector x; /* float x[10] */

#define N 3 typedef double scalar;typedef scalar vector[N];typedef scalar matrix[N][N];

vector w, s; /* 3 elem array of doubles */

matrix b; /* 3x3 array of doubles */

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3. Structures (struct) Sec. 10.13. Structures (struct) Sec. 10.1

3.1. Using structs

3.2. Assignment and Testing

3.3. Combining Type and Variable Declarations

3.4. Student Database

3.5. Initialisation of Structures

3.6. structs are Passed Call by Value

3.7. Arrays (of structs) are Passed Call by Reference

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3.1. Using structs3.1. Using structs

A struct is a way of collecting together a group of data items in a single type.

struct card {int value;char suit; /* 'c','d','h' or 's'

*/};

struct card c1, c2; /* two cards */

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Assignment to the parts:Assignment to the parts:

c1.value = 5;c1.suit = 'd';

c2.value = 12; /* a queen */c2.suit = 's';

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3.2. Assignment and Testing3.2. Assignment and Testing

struct card a, b::

a = b; /* ok */

if (a == b) /* incorrect */. . . ;

Instead write:if (card_equality(a,b))

. . . ;

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int card_equality(struct card a, struct card b)

{ if ((a.value == b.value) && (a.suit == b.suit)) return 1; else return 0;}

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3.3. Combining Type & Variables3.3. Combining Type & Variables

struct card {int value;char suit;

} c, deck[52];

deck[0] deck[1] deck[2] deck[51]

value member suit member

. . . . .

. . . . .

The deck[] array

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The deck[] array:The deck[] array:

deck[0].value = 3;deck[0].suit = 'd'; /* 3 of diamonds */

deck[2].value = 5;deck[2].suit = 'h'; /* 5 of hearts */

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3.4. Student Database3.4. Student Database

/* initialise the class array and calculate the number of fails */#include <stdio.h>

#define CLASS_SIZE 100

struct stude { int student_id; char grade;}

int num_failed(struct stude cls[]);:

continued

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int main(){ struct stude class[CLASS_SIZE];

/* fill in class entries */ class[0].student_id = 590017; class[0].grade = 'A'; class[1].student_id = 230123; class[1].grade = 'B'; : : printf("The number of fails is %d\n", num_failed(class) ); return 0;}

continued

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int num_failed(struct stude cls[])/* How many students got 'F'? */{ int i, cnt = 0;

for (i = 0; i < CLASS_SIZE; i++) cnt += (cls[i].grade == 'F');

return cnt;}

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3.5. Initialisation of Structures3.5. Initialisation of Structures

struct card c = {12, 's'}; /* queen of spades */

struct complex { double real; double imaginary;};

struct complex m[3][3] = {{{1.0, -0.5}, {2.5, 1.0}, {0.7,

0.7}},{{7.0, -6.5}, {-0.5, 1.0}, {45.7,

8.0}}};

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The The m[][]m[][] Array Array

m[0][]

m[1][]

m[2][]

1.0, -0.5 2.5, 1.0 0.7, 0.7

7.0, -6.5 -0.5, 1.0 45.7, 8.0

0.0, 0.0 0.0, 0.0 0.0, 0.0

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3.6. Structs are Passed Call by Value3.6. Structs are Passed Call by Value

/* Try to change a grade */#include <stdio.h>#define CLASS_SIZE 100

struct stude { int student_id; char grade;}

void chg_grade(struct stude s, char grade);

:

continued

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int main(){ struct stude class[CLASS_SIZE];

class[0].student_id = 590017; class[0].grade = 'A'; : chg_grade(class[0], 'B'); /* class[0] grade still 'A' */ return 0;}

continued

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void chg_grade(struct stude s, char grade)

/* change isn't remembered because of call by value passing */{ s.grade = grade;}

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Successfully Change a GradeSuccessfully Change a Grade

#include <stdio.h>#define CLASS_SIZE 100

struct stude { int student_id; char grade;}

struct stude chg_grade(struct stude s, char grade);

:

continued

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int main(){ struct stude class[CLASS_SIZE];

class[0].student_id = 590017; class[0].grade = 'A'; : class[0] = chg_grade(class[0], 'B'); /* class[0] grade now 'B' */ return 0;}

continued

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struct stude chg_grade(struct stude s, char grade)

/* changed student returned */{ s.grade = grade; return s;}

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3.7. Arrays (of Structs) are Passed 3.7. Arrays (of Structs) are Passed Call by ReferenceCall by Reference/* Update a grade by searching the whole array */#include <stdio.h>#define CLASS_SIZE 100

struct stude { int student_id; char grade;}

void update_grade(struct stude cls[], int id, char grade);

continued

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int main(){ struct stude class[CLASS_SIZE];

class[0].student_id = 590017; class[0].grade = 'A'; : update_grade(class, 590017, 'B'); /* class[0] grade now 'B' */

return 0;}

continued

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void update_grade(struct stude cls[], int id, char

grade)/* Change is remembered since arrays are passed using Call by Reference. */{ int count = 0;

while (cls[count].student_id != id) count++;

cls[count].grade = grade;}