Solution to Midterm Exam

• 1. What is the output?#include <stdio.h>main(){ int i, j, k;

i = 2; j = 5; k = 0;

if(i == j) printf("i equals j\n"); else { while(j>k) { printf("%d\n", j); --j; ++k; } }}

543

Solution to Midterm Exam

• 2. What is printed?#define VAL 4#include <stdio.h>main(){ int a[3];

a[0] = 1; a[1] = -1; a[2] = VAL;

printf("%d\n", a[0] < 1 || a[1] != 1);

printf("%d\n", !a[1]); printf("%d\n", a[0] | a[1]); printf("%d\n", a[a[0]+1]);}

1

0

-14

Solution to Midterm Exam

• 3. Write a program that read standard input character by character, and print out the characters to the standard output, replacing spaces ' ' by underscores '\_'. You can use while loop, getchar(), and putchar() functions.

#include <stdio.h>main(){ int c;

while( (c=getchar()) != EOF) { if(c == ' ') putchar('_'); else putchar(c); }}

Quizzes

• What is the output?

#include <stdio.h>main(){ char *s = "ABC xyz"; printf("%s\n", s+4); printf("%c\n", s[4]); printf("%c\n", *s); printf("%s\n", &s);}xyzxAP^U

Quizzes

• What is the output?

#include <stdio.h>int i;void func(int j, int *p, int a[]);main(){ int j, k, *p, a[1]; i = 1; j = 2; k = 3; p = &k; a[0] = 0; func(j, p, a); printf("%d, %d, %d, %d, %d\n", i, j, k, *p,

a[0]);}void func(int j, int *p, int a[]){ i += 10; j += 10; *p += 10; a[0] += 10; p = &i;}

11, 2, 13, 13, 10

Quizzes

• Write a function (with a name of your choice) which take a string and returns an int. If the string looks the same when read forward and backward, return 1, else return 0.

#include <string.h>int palindrome(char *s){ char *e;

e = s + strlen(s) -1; while( s < e ) { if (*s != *e) return 0; ++s; --e; } return 1;}

Looking Toward C++

• Object-Oriented Design is characterized by– Objects (data together with

operations on the data)– Classes (abstract

characterizations of objects)

– Inheritance (code sharing)– Polymorphism (run-time

binding of operations to objects)

Objects• The object-oriented programming

emphasizes objects, which consist of data and operations on the data. For example, we may have a figures like circle or line object with the operation of drawing the figures. If c is a circle object, we invoke its draw method (operation) by passing a message to c:– c.draw()

• While the traditional programming typically call a function like– draw(CIR)

• where CIR is a flag to indicate which figure to draw.

Classes and Abstract Data Type

• A class is an abstract characterization of a set of objects. A class defines variable (data) and methods (operations) common to a set of objects.

• An abstract data type associates operations on the type but hides detail implementation.

Class example• The following code declares a

class string:

class string { char data[80];public: void store(char*); int length();};

• The char data[80] is the data, store() and length() are methods. Only the two methods are accessible to the outside world. The data are private.

Create Objects and Invoke Method

string s, t;• defines two object s and t

belonging to the class string.• Data member is referenced

by writings.xand the method f is invoked

by writing s.f(arguments)

• If ptr is a pointer to s, we use– s -> x or s -> f(arguments)

Pass a Message to Object

class string { char data[80];public: void store(char *); int length();}

string s, t;

s.store("Hi Mom");len = s.length();

The user of the string class need not to know the implementation details.

Inheritance

• A new class can be defined based on an old class. All the data and associated methods becomes part of the new class.

class pen { int x, y; int status;public: void set_status(int); void set_location(int, int);};

class colored_pen: public pen { int color;public: void set_color(int);};

Polymorphism

• Poly : Greek word meaning many.

• Morphism : Greek word meaning form.

• Polymorphism mean many forms. In object-oriented programming, polymorphism refers to identically named methods that have different behavior depending on the type of object that they reference.