python Elementary Programming algorithem

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1
Chapter 2 Elementary Programming

‫وهياكل‬ ‫الخوارزميات‬ ‫هي‬ ‫ما‬
‫البيانات؟‬

‫الخوارزميات‬
‫في‬ ‫ي‬ ‫والت‬ ‫ة‬ ‫والمنطقي‬ ‫ة‬ ‫الرياضي‬ ‫ب‬ ‫التراكي‬ ‫ن‬ ‫م‬ ‫ة‬ ‫مجموع‬
‫أو‬ ‫ج‬ ‫لمنت‬ ‫األداء‬ ‫ين‬ ‫تحس‬ ‫و‬ ‫أ‬ ‫ل‬ ‫مشك‬ ‫ل‬ ‫لح‬ ‫تهدف‬ ‫ة‬ ‫النهاي‬
‫هي‬ ‫وب‬‫الحاس‬ ‫م‬‫عل‬ ‫ي‬‫ف‬ ‫الخوارزميات‬ ،‫ة‬‫المعالج‬ ‫ة‬‫طريق‬
‫واحدة‬ ‫تنفيذها‬ ‫يتم‬ ‫التي‬ ‫الواضحة‬ ‫التعليمات‬ ‫من‬ ‫مجموعة‬
‫لعالم‬ ‫بة‬ ‫نس‬ ‫ظ‬ ‫واللف‬ ،‫ا‬ ‫م‬ ‫ة‬ ‫مشكل‬ ‫ل‬ ‫لح‬ ‫اآلخرى‬ ‫و‬ ‫تل‬
.‫الخوارزمي‬ ‫موسى‬ ‫بن‬ ‫محمد‬ ‫الرياضيات‬

‫وهياكل‬ ‫الخوارزميات‬ ‫هي‬ ‫ما‬

‫البيانات‬ ‫هياكل‬
‫فى‬ ‫التخزين‬ ‫عملية‬ ‫تصميم‬ ‫على‬ ‫تعتمد‬ ‫البيانات‬ ‫هياكل‬
‫نوع‬ ‫ليدعم‬ ،‫معقدة‬ ‫ر‬‫وغي‬ ‫فعالة‬ ‫بطريقة‬ ‫بيوتر‬‫الكم‬
‫او‬ ‫البرمجة‬ ‫شيفرة‬ ‫ل‬‫لتعم‬ ‫ا‬‫تخزينه‬ ‫المراد‬ ‫بيانات‬‫ال‬
.‫كفاءة‬ ‫وأكثر‬ ‫اسرع‬ ‫بطريقة‬ ‫الخوارزميات‬

‫وهياكل‬ ‫الخوارزميات‬ ‫نتعلم‬ ‫لماذا‬
)1
‫تفكيرك‬ ‫طريقة‬ ‫تحسن‬
o
‫تكتبه‬ ‫الذي‬ ‫البرمجي‬ ‫للكود‬ ‫ادراكا‬ ‫أكثر‬ ‫تصبح‬ ‫حيث‬
)2
‫وتنظيمها‬ ‫األفكار‬ ‫وضوح‬
)3
‫مصادر‬ ‫وأقل‬ ‫بفاعلية‬ ‫المشاكل‬ ‫حل‬
)4
‫العمل‬ ‫مقابالت‬ ‫في‬ ‫النجاح‬

‫البيانات‬ ‫وهياكل‬ ‫الخوارزميات‬ ‫أهم‬

– ‫القوائم‬
Lists

– ‫المتصلة‬ ‫القوائم‬
Linked Lists

– ‫المكدسات‬
Stacks

– ‫الطوابير‬
Queues

– ‫الشجرات‬
Trees

– ‫البحث‬
Searching

– ‫الفرز‬
Sorting

‫البيانات‬ ‫وهياكل‬ ‫الخوارزميات‬ ‫أهمية‬
‫البرنامج‬
Program Code
‫بيانات‬
Data
‫األوامر‬
Instructions
‫من‬ ‫يتكون‬


‫مثال‬
:
Method
Add(a, b)
{
return a + b;
}
Data – ‫البيانات‬:
•a
•b
Instructions – ‫األوامر‬:
•Return
•+

CPU
RAM
Storage Memory
Code
(Instructions)
Data
‫المستخدمة‬ ‫بيانات‬55‫وال‬ ‫برنامج‬55‫ال‬
‫التخزين‬ ‫وحدة‬ ‫ل‬5‫خ‬‫دا‬ ‫ة‬5‫ن‬‫مخز‬ ‫تكون‬
) (
‫ديسك‬ ‫هارد‬

CPU
Storage Memory
Code
(Instructions)
Data
( ‫ل‬5‫ي‬‫لتشغ‬
run
)
‫ال‬ ‫يقوم‬ ‫البرنامج‬
CPU
‫الى‬ ‫الكود‬ ‫خ‬5‫س‬‫ن‬ ‫و‬5‫أ‬ ‫ل‬5‫ي‬‫بتحم‬
( ‫العشوائية‬ ‫الذاكرة‬
RAM
)

CPU
Storage Memory
Code
(Instructions)
Data
Code
(Instructions)
‫ال‬ ‫يقوم‬ ‫الكود‬ ‫تشغيل‬ ‫أثناء‬
CPU
( ‫الالزمة‬ ‫بيانات‬5‫ل‬‫ا‬ ‫ل‬5‫ي‬‫بتحم‬
Data
)
‫أيضا‬ ‫العشوائية‬ ‫الذاكرة‬ ‫الى‬

CPU
Storage Memory
Code
(Instructions)
Data
Code
(Instructions)
Data
5‫ل‬‫العم‬ ‫برنامج‬55‫ال‬ ‫تطيع‬55‫يس‬ ‫االن‬
‫أفضل‬ ‫وفاعلية‬ ‫بسرعة‬

CPU
Storage Memory
Code
(Instructions)
Data
Code
(Instructions)
Data
‫البيانات‬ ‫تدعاء‬55‫باس‬ ‫الكود‬ ‫يقوم‬
‫العشوائية‬ ‫الذاكرة‬ ‫ي‬55‫ف‬ ‫ة‬55‫المخزن‬
‫البرنامج‬ ‫عمل‬ ‫اثناء‬

CPU
Storage Memory
Code
(Instructions)
Data
Code
(Instructions)
Data
‫البيانات‬ ‫ل‬5‫هياك‬ ‫ة‬5‫اهمي‬ ‫ن‬5‫تكم‬ ‫ا‬5‫هن‬
(
Data Structure
)
‫خالل‬ ‫من‬
‫في‬ ‫بيانات‬5‫ل‬5‫ا‬ ‫ن‬5‫ي‬‫تخز‬ ‫ة‬5‫ي‬‫وال‬ ‫ة‬5‫ق‬‫طري‬
‫العشوائية‬ ‫الذاكرة‬

CPU
Storage Memory
Code
(Instructions)
Data
Code
(Instructions)
Data
( ‫البيانات‬ ‫ل‬5‫ك‬‫هيا‬ ‫ف‬5‫ي‬‫تعر‬ ‫ن‬5‫ك‬‫يم‬
Data
Structure
)
‫طريقة‬ ‫ا‬55‫أنه‬ ‫ى‬55‫عل‬
‫المستخدمة‬ ‫بيانات‬5‫ال‬ ‫ن‬5‫وتخزي‬ ‫ب‬5‫لترتي‬
‫أكثر‬ ‫ل‬5‫بشك‬ ‫تخدامها‬5‫باس‬ ‫مح‬5‫تس‬ ‫ة‬5‫بالي‬
‫من‬ ‫برنامج‬55‫ال‬ ‫ن‬55‫تمك‬ ‫ا‬55‫كم‬ ،‫ة‬55‫فعالي‬
‫أقصر‬ ‫ووقت‬ ‫بسهولة‬ ‫اليها‬ ‫الوصول‬

15
Introducing Programming with an
Example
Listing 2.1 Computing the Area of a
Circle
This program computes the area of the
circle.
ComputeArea

Algorithms and Data Structures
‫البيانات‬ ‫وهياكل‬ ‫الخوارزميات‬
#
#
02
02
‫الذاكرة‬ ‫تخصيص‬ –
‫الذاكرة‬ ‫تخصيص‬ –

‫الذاكرة‬ ‫تخصيص‬
‫الذاكرة‬ ‫تخصيص‬
(Memory Allocation)
(Memory Allocation)
•
)‫وأوامر‬ ‫(بيانات‬ ‫ما‬ ‫لعملية‬ ‫الذاكرة‬ ‫عنوان‬ ‫مساحة‬ ‫لتخصيص‬ ‫إجراء‬
‫لتنفيذها‬
•
‫الذاكرة‬ ‫تخصيص‬ ‫أنواع‬
.1
‫الثابت‬ ‫الذاكرة‬ ‫تخصيص‬
Static Memory Allocation
.2
‫الديناميكي‬ ‫الذاكرة‬ ‫تخصيص‬
Dynamic Memory Allocation

•
‫الثابت‬ ‫الذاكرة‬ ‫تخصيص‬
Static Memory Allocation
o
( ‫م‬5‫المترج‬ ‫يقوم‬ ‫ا‬5‫عندم‬ ‫ت‬5‫الثاب‬ ‫الذاكرة‬ ‫يص‬5‫تخص‬ ‫ذ‬5‫ي‬‫تنف‬ ‫م‬5‫يت‬
Compiler
‫ع‬5‫بتجمي‬ )
‫ر‬5‫العناص‬ ‫ملفات‬ ‫ع‬5‫جمي‬ ‫ج‬5‫بدم‬ ‫ط‬5‫الراب‬ ‫ويقوم‬ ،‫ر‬5‫العناص‬ ‫ملفات‬ ‫وإنشاء‬ ‫برنامج‬5‫ال‬
‫للتنفيذ‬ ‫قابل‬ ‫واحد‬ ‫ملف‬ ‫وإنشاء‬ ‫هذه‬

•
‫الديناميكي‬ ‫الذاكرة‬ ‫تخصيص‬
o
‫يص‬5‫ص‬‫تخ‬ ‫م‬5‫ت‬‫ي‬ ،‫ا‬5‫ن‬‫ه‬ ،‫برنامج‬5‫ل‬‫ا‬ ‫ذ‬5‫ي‬‫تنف‬ ‫أثناء‬ ‫ي‬5‫ك‬‫الدينامي‬ ‫الذاكرة‬ ‫يص‬5‫ص‬‫تخ‬ ‫ذ‬5‫ي‬‫تنف‬ ‫م‬5‫ت‬‫ي‬
،‫البرنامج‬ ‫تشغيل‬ ‫أثناء‬ ‫مرة‬ ‫ألول‬ ‫استخدامها‬ ‫يتم‬ ‫عندما‬ ‫البرنامج‬ ‫لعناصر‬ ‫الذاكرة‬
‫ص‬5‫يخص‬ ‫و‬5‫فه‬ ‫لذا‬ ،‫ل‬5‫التشغي‬ ‫ت‬5‫وق‬ ‫ي‬5‫ف‬ ‫ة‬5‫المطلوب‬ ‫بيانات‬5‫لل‬ ‫ي‬5‫الفعل‬ ‫م‬5‫الحج‬ ‫عرف‬ُ
‫ي‬
‫الذاكرة‬ ‫إهدار‬ ‫من‬ ‫يقلل‬ ‫وبالتالي‬ ‫للبرنامج‬ ‫الدقيقة‬ ‫الذاكرة‬ ‫مساحة‬

‫الذاكرة‬ ‫تخصيص‬ ‫فهم‬
CPU
Storage
Memory
Code
(Instructions)
Data
( ‫ة‬5‫ي‬‫لعشوائ‬5‫ا‬ ‫الذاكرة‬ ‫م‬5‫س‬‫تق‬
RAM
)
‫أقسام‬ ‫ثالثة‬ ‫الى‬
Code
Stack
Heap

CPU
Storage
Memory
Code
(Instructions)
Data
‫جزء‬ ‫في‬ ‫البرنامج‬ ‫كود‬ ‫تحميل‬ ‫يتم‬
‫الذاكرة‬ ‫في‬ ‫الكود‬
Code
Code
Stack
Heap
Code
(Instructions)

CPU
Storage
Memory
Code
(Instructions)
Data
‫يحتوي‬ ‫البرنامج‬ ‫ان‬ ‫فرض‬ ‫على‬:
main()
{
int n1, n2;
float Avg;
Avg = (n1+n2) / 2;
}
Code
Stack
Heap
Code
(Instructions)
( ‫البيانات‬ ‫نوع‬ ‫معروف‬ ‫يكون‬ ‫عندما‬
Primitive Data Type
)
‫للمتغيرات‬ ‫المحجوزة‬ ‫لمساحة‬5‫ا‬ ‫معروف‬ ‫يكون‬
n1 n2
Avg

CPU
Storage
Memory
Code
(Instructions)
Data
main()
{
int n1, n2;
n1 = 5; n2 = 10;
float Avg;
Avg = (n1+n2) / 2;
}
Code
Stack
Heap
Code
(Instructions)
‫يتم‬ ‫معروفة‬ ‫المحجوزة‬ ‫والمساحة‬ ‫معروف‬ ‫البيانات‬ ‫نوع‬ ‫أن‬ ‫بما‬
( ‫قسم‬ ‫في‬ ‫المساحة‬ ‫حجز‬
Stack
‫الذاكرة‬ ‫من‬ )
n1 n2
Avg

CPU
Storage
Memory
Code
(Instructions)
Data
main()
{
int n1, n2;
n1 = 5; n2 = 10;
float Avg;
Avg = (n1+n2) / 2;
}
Code
Stack
Heap
Code
(Instructions)
( ‫قسم‬ ‫في‬ ‫للمتغيرات‬ ‫المساحة‬ ‫حجز‬ ‫يتم‬
Stack
‫في‬ ‫الذاكرة‬ ‫من‬ )
( ‫ال‬ ‫مرحلة‬
Compilation
‫البرنامج‬ ‫تنفيذ‬ ‫مرحلة‬ ‫قبل‬ )
5 10
n1 n2
7.5
Avg

‫الذاكرة‬ ‫تخصيص‬ ‫مثال‬
‫الذاكرة‬ ‫تخصيص‬ ‫مثال‬
Memory
main()
{
int i;
float * ptr;
cout << “Enter array size
n”;
cin >> i;  ex: 5
ptr = new float [i];
delete [] ptr;
return 0;
} Code
Stack
Heap
Code
*
i ptr
Main
( ‫في‬ ‫الديناميكي‬ ‫كرة‬5‫ا‬‫الذ‬ ‫حجز‬ ‫يوضح‬ ‫المثال‬ ‫هذا‬
Heap
‫من‬ )
( ‫البرنامج‬ ‫تنفيذ‬ ‫مرحلة‬ ‫في‬ ‫الذاكرة‬
Run
)

#
#
03
03
‫تصنيفات‬ –
‫تصنيفات‬ –

‫البيانات‬ ‫هياكل‬ ‫تصنيفات‬
•
o
.‫فعال‬ ‫بشكل‬ ‫استخدامها‬ ‫ليتم‬ ‫الحاسوب‬ ‫في‬ ‫البيانات‬ ‫وتنظيم‬ ‫لترتيب‬ ‫خاصة‬ ‫طريقة‬
o
.‫واحد‬ ‫اسم‬ ‫تحت‬ ‫البعض‬ ‫بعضها‬ ‫مع‬ ‫تخزينها‬ ‫يتم‬ ‫البيانات‬ ‫عناصر‬ ‫من‬ ‫مجموعة‬
•
( ‫المصفوفة‬ :‫مثال‬
Array
)
.‫النوع‬ ‫نفس‬ ‫من‬ ‫عناصر‬ ‫عدة‬ ‫يحتوي‬ –
•
– ‫أيضا‬ ‫عليها‬ ‫يطلق‬
Abstract Data Type (ADT)
o
‫البيانات‬ ‫تخزين‬ ‫طريقة‬
o
‫البيانات‬ ‫هذه‬ ‫على‬ ‫تتم‬ ‫التي‬ ‫والعمليات‬ ‫األوامر‬

•
( ‫مثال‬
ADT
– ‫الطابور‬ :)
Queue
Counter
Front
or
Head
Rear
or
Tail
enqueue dequeue

•
‫البيانات‬ ‫هياكل‬ ‫استخدام‬ ‫من‬ ‫الهدف‬
o
:‫على‬ ‫يساعد‬
•
‫فعال‬ ‫بشكل‬ ‫البيانات‬ ‫تخزين‬
•
‫ممكن‬ ‫وقت‬ ‫أقل‬ ‫في‬ ‫البيانات‬ ‫استرجاع‬
•
‫فعال‬ ‫بشكل‬ ‫البيانات‬ ‫تعديل‬
•
‫البرنامج‬ ‫تصميم‬ ‫أثناء‬
o
( ‫البيانات‬ ‫هياكل‬ ‫من‬ ‫نوع‬ ‫أنسب‬ ‫ختيار‬5‫ا‬ ‫هو‬ ‫التحدي‬
Data Structure
‫ما‬ ‫مشكلة‬ ‫لحل‬ )
•
( ‫ال‬ ‫استخدام‬ ‫يفضل‬ ‫ال‬ ‫الطالب‬ ‫عالمات‬ ‫الدخال‬ :‫مثال‬
Array
.‫ثابت‬ ‫حجمها‬ ‫الن‬ )

•

•
‫الوجود‬ ‫حسب‬ ‫التصنيف‬
o
‫المادية‬ ‫البيانات‬ ‫هياكل‬
(
Physical
)
•
‫مستقل‬ ‫بشكل‬ ‫انشائها‬ ‫يمكن‬
o
( ‫المصفوفات‬
Array
)
o
( ‫المتصلة‬ ‫القوائم‬
Linked List
)
o
‫المنطقية‬ ‫البيانات‬ ‫هياكل‬
(
Logical
)
•
‫مستقل‬ ‫بشكل‬ ‫انشائها‬ ‫يمكن‬ ‫ال‬
o
( ‫المكدسات‬
Stacks
)
o
( ‫الطوابير‬
Queues
)
o
( ‫الشجرات‬
Trees
)

•
‫الذاكرة‬ ‫حجز‬ ‫حسب‬ ‫التصنيف‬
o
( ‫المساحة‬ ‫ثابتة‬ ‫البيانات‬ ‫هياكل‬
Static
)
•
‫ثابتة‬ ‫مساحة‬ ‫تحجز‬
•
( ‫المصفوفات‬ ‫مثل‬
Array
)
o
( ‫المساحة‬ ‫ديناميكية‬ ‫البيانات‬ ‫هياكل‬
Dynamic
)
•
‫الحاجة‬ ‫حسب‬ ‫المساحة‬ ‫تتغير‬
•
( ‫المتصلة‬ ‫القوائم‬ ‫مثل‬
Linked List
)

•
5
‫ل‬‫التمثي‬ ‫حسب‬ ‫التصنيف‬
o
( ‫الخطية‬ ‫البيانات‬ ‫هياكل‬
Linear
)
•
( ‫المصفوفات‬
Array
)
•
( ‫المتصلة‬ ‫القوائم‬
Linked List
)
•
( ‫المكدسات‬
Stack
)
•
( ‫الطابور‬
Queue
)
o
( ‫الخطية‬ ‫غير‬ ‫البيانات‬ ‫هياكل‬
Non-Linear
)
•
( ‫الشجرات‬
Trees
)
•
( ‫البياني‬ ‫الرسم‬
Graph
)

‫البيانات‬ ‫هياكل‬ ‫على‬ ‫العمليات‬
•
– 5
‫ر‬‫العناص‬ ‫جميع‬ ‫على‬ ‫المرور‬
Traversing
o
.‫العنصر‬ ‫هذا‬ ‫على‬ ‫ما‬ ‫عملية‬ ‫وتنفيذ‬ ‫عنصر‬ ‫كل‬ ‫زيارة‬ ‫أو‬ ‫الوصول‬
•
- ‫البحث‬
Searching
o
.‫البيانات‬ ‫تركيب‬ ‫في‬ ‫مخزن‬ ‫معين‬ ‫عنصر‬ ‫موقع‬ ‫تحديد‬ ‫أو‬ ‫البحث‬
•
– ‫االضافة‬
Insertion
o
.‫موجود‬ ‫بيانات‬ ‫تركيب‬ ‫الى‬ ‫جديد‬ ‫عنصر‬ ‫اضافة‬

•
– ‫الحذف‬
Deletion
o
.‫موجود‬ ‫بيانات‬ ‫تركيب‬ ‫من‬ ‫عنصر‬ ‫ازالة‬ ‫أو‬ ‫حذف‬
•
– ‫الترتيب‬
Sorting
o
.‫منطقية‬ ‫بطريقة‬ ‫البيانات‬ ‫تركيب‬ ‫في‬ ‫العناصر‬ ‫ترتيب‬
•
.‫تنازلي‬ ‫أو‬ ‫تصاعدي‬ ‫ترتيبها‬ ‫يمكن‬
•
– ‫الدمج‬
Merging
o
.‫واحد‬ ‫في‬ ‫وجمعها‬ ‫بيانات‬ ‫تركيب‬ ‫من‬ ‫أكثر‬ ‫من‬ ‫العناصر‬ ‫ودمج‬ ‫ضم‬

36
Trace a Program Execution
# Assign a radius
radius = 20 # radius is now 20
# Compute area
area = radius * radius * 3.14159
# Display results
print("The area for the circle of radius",
radius, "is", area)
20
radius
Assign 20 to radius
animation

37
# Assign a radius
# Compute area
# Display results
radius, "is", area)
20
radius
Assign result to
area
animation
1256.636
area

38
# Assign a radius
# Compute area
# Display results
radius, "is", area)
20
radius
print a message to
the console
animation
1256.636
area

39
Reading Input from the Console
1. Use the input function
variable = input("Enter a string: ")
2. Use the float and int function to convert a string to a float
or int.
var = float(stringVariable)
var = int(stringVariable)
ComputeAreaWithConsoleInput
ComputeAverage

40
Identifiers
 An identifier is a sequence of characters that
consists of letters, digits, underscores (_), and
asterisk (*).
 An identifier must start with a letter or an
underscore. It cannot start with a digit.
 An identifier cannot be a reserved word. (See
Appendix A, "Python Keywords," for a list of
reserved words.) Reserved words have special
meanings in Python, which we will later discuss.
 An identifier can be of any length.

41
Variables
# Compute the first area
radius = 1.0
print("The area is ", area,
" for radius ", radius)
# Compute the second area
radius = 2.0
print("The area is ", area,
" for radius ", radius)

42
Expression
x = 1 # Assign 1 to variable x
radius = 1.0 # Assign 1.0 to variable radius
# Assign the value of the expression to x
x = 5 * (3 / 2) + 3 * 2
x = y + 1 # Assign the addition of y and 1 to x
area = radius * radius * 3.14159 # Compute area

43
Assignment Statements
x = 1 # Assign 1 to x
x = x + 1
i = j = k = 1

44
Simultaneous Assignment
var1, var2, ..., varn = exp1, exp2, ..., expn
x, y = y, x # Swap x with y
ComputeAverageWithSimultaneousAssignment

45

46
Named Constants
The value of a variable may change during the
execution of a program, but a named constant or
simply constant represents permanent data that
never changes. Python does not have a special
syntax for naming constants. You can simply
create a variable to denote a constant. To
distinguish a constant from a variable, use all
uppercase letters to name a constant.

47
Numerical Data Types
 integer: e.g., 3, 4
 float: e.g., 3.0, 4.0

48
Numeric Operators
Name Meaning Example Result
+ Addition 34 + 1 35
- Subtraction 34.0 – 0.1 33.9
* Multiplication 300 * 30 9000
/ Float Division 1 / 2 0.5
// Integer Division 1 // 2 0
** Exponentiation 4 ** 0.5 2.0
% Remainder 20 % 3 2

49
The % Operator
12
4
3
12
0
7
3
2
6
1
26
8
3
24
2 Remainder
Quotient
20
13
1
13
7
Dividend
Divisor

50
Remainder Operator
Remainder is very useful in programming. For example, an
even number % 2 is always 0 and an odd number % 2 is always
1. So you can use this property to determine whether a number
is even or odd. Suppose today is Saturday and you and your
friends are going to meet in 10 days. What day is in 10
days? You can find that day is Tuesday using the following
expression:
Saturday is the 6th
day in a week
A week has 7 days
After 10 days
The 2nd
day in a week is Tuesday
(6 + 10) % 7 is 2

51
Problem: Displaying Time
Write a program that obtains minutes and
remaining seconds from seconds.
DisplayTime

52
Overflow
When a variable is assigned a value that is too
large (in size) to be stored, it causes overflow.
For example, executing the following
statement causes overflow.
>>> 245.0 ** 1000
OverflowError: 'Result too large'

53
Underflow
When a floating-point number is too small (i.e., too
close to zero) to be stored, it causes underflow.
Python approximates it to zero. So normally you
should not be concerned with underflow.

54
Scientific Notation
Floating-point literals can also be specified in
scientific notation, for example, 1.23456e+2,
same as 1.23456e2, is equivalent to 123.456, and
1.23456e-2 is equivalent to 0.0123456. E (or e)
represents an exponent and it can be either in
lowercase or uppercase.

55
Arithmetic Expressions
)
9
4
(
9
)
)(
5
(
10
5
4
3
y
x
x
x
c
b
a
y
x 







is translated to
(3+4*x)/5 – 10*(y-5)*(a+b+c)/x + 9*(4/x + (9+x)/y)

56
How to Evaluate an Expression
Though Python has its own way to evaluate an
expression behind the scene, the result of a Python
expression and its corresponding arithmetic expression
are the same. Therefore, you can safely apply the
arithmetic rule for evaluating a Python expression.
3 + 4 * 4 + 5 * (4 + 3) - 1
3 + 4 * 4 + 5 * 7 – 1
3 + 16 + 5 * 7 – 1
3 + 16 + 35 – 1
19 + 35 – 1
54 - 1
53
(1) inside parentheses first
(2) multiplication
(3) multiplication
(4) addition
(6) subtraction
(5) addition

57
Augmented Assignment Operators
Operator Example Equivalent
+= i += 8 i = i + 8
-= f -= 8.0 f = f - 8.0
*= i *= 8 i = i * 8
/= i /= 8 i = i / 8
//= i //= 8 i = i // 8
%= i %= 8 i = i % 8
**= i **= 8 i = i ** 8

58
Type Conversion and Rounding
datatype(value)
i.e., int(4.5) => 4
float(4) => 4.0

59
Problem: Keeping Two Digits After
Decimal Points
Write a program that displays the sales tax with two
digits after the decimal point.
SalesTax

60
Problem: Displaying Current Time
Write a program that displays current time in GMT in the
format hour:minute:second such as 1:45:19.
The time.time() function returns the current time in seconds
with millisecond precision since the midnight, January 1,
1970 GMT. (1970 was the year when the Unix operating
system was formally introduced.) You can use this function
to obtain the current time, and then compute the current
second, minute, and hour as follows.
Elapsed
time
Unix epoch
01-01-1970
00:00:00 GMT
Current time
Time
time.time()
ShowCurrentTime

61
Problem:
Computing Loan Payments
This program lets the user enter the interest
rate, number of years, and loan amount, and
computes monthly payment and total
payment.
12
)
1
(
1
1 




ars
numberOfYe
erestRate
monthlyInt
erestRate
monthlyInt
loanAmount
ment
monthlyPay
ComputeLoan

62
Case Study: Computing Distances
This program prompts the user to enter two
points, computes their distance, and displays
the distance.
2
1
2
2
1
2 )
(
)
( y
y
x
x 


ComputeDistance

63
Case Study: Computing Distances
This program prompts the user to enter two
points, computes their distance, and displays
the points and their distances in graphics.
ComputeDistanceGraphics

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