TK 1914 : C++ Programming Algorithms and Problem Solving
WHAT IS AN ALGORITHM? • An algorithm is a set of ordered steps for solving a problem. • Examples: • An algorithm for preparing breakfast. • An algorithm for converting Gregorian dates to Islamic dates. • An algorithm for calculating moon phase. • An algorithm for drawing a curve. FTSM : : TK 1914 20112012 2
ALGORITHM IN REAL LIFE • Consider the following … Problem: Baking a Cake How to solve: 1. Start 2. Preheat the oven at 180 o. C 3. Prepare a baking pan 4. Beat butter with sugar 5. Mix them with flour, eggs and essence vanilla 6. Pour the dough into the baking pan 7. Put the pan into the oven 8. End FTSM : : TK 1914 20112012 3
‘DIVIDE AND CONQUER’ STRATEGY IN ALGORITHM Problem: Prepare a Breakfast 1. Start 2. Prepare a Breakfast 3. End FTSM : : TK 1914 20112012 4
‘DIVIDE AND CONQUER’ STRATEGY IN ALGORITHM 1. Start 2. Prepare a Breakfast 2. 1 Prepare a tuna sandwich 2. 2 Prepare some chips 2. 3 Make a cup of coffee 3. End FTSM : : TK 1914 20112012 5
‘DIVIDE AND CONQUER’ STRATEGY IN ALGORITHM 1. Start 2. Prepare a Breakfast 2. 1 Prepare a tuna sandwich 2. 1. 1 Take 2 slices of bread 2. 1. 2 Prepare tuna paste 2. 2 Prepare some chips 2. 3 Make a cup of coffee 3. End FTSM : : TK 1914 20112012 6
‘DIVIDE AND CONQUER’ STRATEGY IN ALGORITHM 1. Start 2. Prepare a Breakfast 2. 1 Prepare a tuna sandwich 2. 1. 1 Take 2 slices of bread 2. 1. 2 Prepare tuna paste 2. 2 Prepare some chips 2. 2. 1 Cut potatoes into slices 2. 2. 2 Fry the potatoes 2. 3 Make a cup of coffee 3. End FTSM : : TK 1914 20112012 7
‘DIVIDE AND CONQUER’ STRATEGY IN ALGORITHM 1. Start 2. Prepare a Breakfast 2. 1. Prepare a tuna sandwich 2. 1. 1 Take 2 slices of bread 2. 1. 2 Prepare tuna paste 2. 2. Prepare some chips 2. 2. 1 Cut potatoes into slices 2. 2. 2 Fry the potatoes 2. 3. Make a cup of coffee 2. 3. 1 Boil water 2. 3. 2 Add water with sugar and coffee 3. End FTSM : : TK 1914 20112012 8
CLASS ACTIVITY 5. 1 • Write a simple algorithm for withdrawing a sum of money at an ATM. FTSM : : TK 1914 20112012 9
WHY DO WE NEED TO BUILD ALGORITHMS? • If we wish to build a house, we need to design it first. – Can you think of some possible consequences of not designing a house before building it? • Similarly, computer programs (especially large and complex ones) need to be designed before they are written. – Can you think of some possible consequences of not designing a program before building it? • One of the things considered when designing a computer program is the algorithm which it will be based on. FTSM : : TK 1914 20112012 10
ALGORITHMS IN PROGRAM DESIGN • A computer program is built to solve a certain problem. Examples: 1. A program to calculate the grade obtained given a mark. 2. A program to convert a Gregorian date to an Islamic date. 3. A program to produce a document. FTSM : : TK 1914 20112012 11
• Below are steps (in fact, an algorithm) for building a program to solve a particular problem: – Analyse the problem – Design a computer solution to the problem by developing an algorithm. – Write a computer program based on the algorithm. – Test the program. FTSM : : TK 1914 20112012 12
HOW TO SPECIFY AN ALGORITHM? • An algorithm must be specific enough so that it can be conveniently translated into a computer program (using C++, for example). • An algorithm can be specified: – Textually For example, using pseudo code (see later) – Graphically For example, using flowcharts or UML activity charts FTSM : : TK 1914 20112012 13
FLOWCHARTS • A flowchart is a graphical representation of the sequence of operations in a program. • An algorithm can be represented graphically using a flowchart. FTSM : : TK 1914 20112012 14
FLOWCHART NOTATIONS Symbol Semantic Start/End Process Input/Output Test Connector Flow of activities FTSM : : TK 1914 20112012 15
FLOWCHART: EXAMPLE 1 Start Algorithm starts here Input Gregorian date Input data from user Convert Gregorian date to Islamic date Perform the date conversion Display Islamic date Display the result Algorithm ends here End FTSM : : TK 1914 20112012 16
PSEUDOCODE • An outline of a program, written in a form that can easily be converted into real programming statements. It resembles the actual program that will be implemented later. However, it cannot be compiled nor executed. • Pseudocode normally codes the following actions: – Initialisation of variables – Assignment of values to the variables – Arithmetic operations – Relational operations FTSM : : TK 1914 20112012 17
EXAMPLE OF PSEUDOCODE 1. Start 2. Read quantity 3. Read price_per_kg 4. price quantity * price_per_kg 5. Print price 6. End FTSM : : TK 1914 20112012 18
CLASS ACTIVITY 5. 2 • Draw a flowchart which represents the algorithm built in CA[5. 1]. FTSM : : TK 1914 20112012 19
FLOWCHART: EXAMPLE 2 Start Input length, width area ← length X width • length, width and area are referred to as variables. • A variable is like a box in which a value can be stored Output area End FTSM : : TK 1914 20112012 20
FLOWCHART: EXAMPLE 3 • Selection Start Input height false height > 1. 6? Output “You are short!” true Output “You are tall!” End FTSM : : TK 1914 20112012 21
FLOWCHART: EXAMPLE 4 • Repetition (looping) Start Output “Thank you!” Input stop = 1? false true End FTSM : : TK 1914 20112012 22
PROBLEM SOLVING FTSM : : TK 1914 20112012 23
PROBLEM SOLVING • Programming is a process of problem solving • Problem solving techniques – Analyze the problem – Outline the problem requirements – Design steps (algorithm) to solve the problem • Algorithm: – Step-by-step problem-solving process – Solution achieved in finite amount of time FTSM : : TK 1914 20112012 24
PROBLEM SOLVING PROCESS • Step 1 - Analyze the problem – Outline the problem and its requirements – Design steps (algorithm) to solve the problem • Step 2 - Implement the algorithm – Implement the algorithm in code – Verify that the algorithm works • Step 3 - Maintenance – Use and modify the program if the problem domain changes FTSM : : TK 1914 20112012 25
EXAMPLE 1: RECTANGLE • Problem: Design an algorithm to find the perimeter and area of a rectangle. • Information: The perimeter and area of the rectangle are given by the following formulas: perimeter = 2 * (length + width) area = length * width FTSM : : TK 1914 20112012 26
EXAMPLE 1 • Requirements: – Input: length and width of the rectangle – Output: perimeter and area of the rectangle – Process: perimeter = ? ? ? , area =? ? ? FTSM : : TK 1914 20112012 27
EXAMPLE 1 • Algorithm: – Get length of the rectangle – Get width of the rectangle – Find the perimeter using the following equation: perimeter = 2 * (length + width) – Find the area using the following equation: area = length * width – Display the result perimeter and area FTSM : : TK 1914 20112012 28
EXAMPLE 2: CALCULATE CAR PARK CHARGE A car park has the following charges: The 1 st hour costs RM 2. 00. The subsequent hours cost RM 1. 00 per hour. Write an algorithm to calculate the charges based on a vehicle’s entry and exit time. Input • Entry_time • Exit_time Process ? ? FTSM : : TK 1914 20112012 Output Charge 29
EXAMPLE 2: FLOWCHART Start Input Entry_time Input Exit_time Period Exit_time – Entry_time Charge 2 No Yes Charge 2 + (Period * 1) Period > 1? Output Charge End FTSM : : TK 1914 20112012 30
EXAMPLE 2: FLOWCHART Start Input Entry_time Input Exit_time Period Exit_time – Entry_time Charge 2 cin >> entry_time >> exit_ti period = exit_time – entry_t Period > 1? Charge 2 + (Period * 1) No Yes Output Charge if (period > 1) charge = 2 + ( period End *1); else charge = 2; FTSM : : TK 1914 20112012 cout <<charge; 31
EXAMPLE 2: C++ PROGRAM void main() { int entry_time, exit_time, period, charge; cin >>entry_time >>exit_time; period = exit_time – entry_time; if (period > 1) charge = 2 + (period * 1); else charge = 2; cout <<charge; } FTSM : : TK 1914 20112012 32
EXAMPLE 3: PAYCHECK • Problem: Design an algorithm to calculate a paycheck of a salesperson. • Information: – Every salesperson has a base salary. – Salesperson receives $10 bonus at the end of the month for each year worked if he or she has been with the store for five or less years. – The bonus is $20 for each year that he or she has worked there if over 5 years. FTSM : : TK 1914 20112012 33
EXAMPLE 3 • Information (continue): Additional bonuses are as follows: – If total sales for the month are $5, 000 -$10, 000, he or she receives a 3% commission on the sale – If total sales for the month are at least $10, 000, he or she receives a 6% commission on the sale FTSM : : TK 1914 20112012 34
EXAMPLE 3 • Requirements: – Input: base salary, number of years work, total sale – Output: amount of paycheck (total salary) – Process: ? ? ? FTSM : : TK 1914 20112012 35
EXAMPLE 3 • Algorithm: – Get base. Salary – Get no. Of. Service. Years – Calculate bonus using the following formula: if (no. Of. Service. Years <= 5) bonus = 10 * no. Of. Service. Years otherwise bonus = 20 * no. Of. Service. Years – Get total. Sale FTSM : : TK 1914 20112012 36
EXAMPLE 3 – Calculate additional. Bonus as follows: if (total. Sale < 5000) additional. Bonus = 0 otherwise if (total. Sale>=5000 and total. Sale<10000) additional. Bonus = total. Sale x(0. 03) otherwise additional. Bonus = total. Sale x (0. 06) FTSM : : TK 1914 20112012 37
EXAMPLE 3 – Calculate pay. Check using the equation pay. Check = base. Salary + bonus + additional. Bonus FTSM : : TK 1914 20112012 38
EXAMPLE 4: AVERAGE TEST SCORE • Problem: – 10 students in a class – Each student has taken five tests and each test is worth 100 points. – Design an algorithm to calculate the grade for each student as well as the class average. • Design an algorithm to find the average test score. • Design an algorithm to determine the grade. – Data consists of students’ names and their test scores. FTSM : : TK 1914 20112012 39
EXAMPLE 4 • Algorithm 1: to find test score – Get the five test scores. – Add the five test scores. Suppose sum stands for the sum of the test scores. – Suppose average stands for the average test score. Then average = sum / 5; FTSM : : TK 1914 20112012 40
EXAMPLE 4 • Algorithm 2: to determine the grade. if average > 90 grade = A otherwise if average >= grade = otherwise grade = 80 and < 90 B 70 and < 80 C 60 and < 70 D F FTSM : : TK 1914 20112012 41
EXAMPLE 4 • Main algorithm: – total. Average = 0; – Repeat the following steps for each student in the class. • Get student’s name. • Use algorithm 1. • Use the algorithm 2. • Update total. Average by adding current student’s average test score. – Determine the class average as follows: class. Average = total. Average / 10 FTSM : : TK 1914 20112012 42
PROGRAM STYLE AND FORM FTSM : : TK 1914 20112012 43
USE OF WHITESPACE • Insert white space characters (such as blanks, tabs and newlines) if necessary to increase the readability of your source code. Example: int matrix[][3] = {1, 0, 0, 0, 1}; int matrix[][3] = { 1, 0, 0, 0, 1 }; • White space characters are ignored by the compiler during compilation. • Remember to separate reserved words and identifiers This statement from each other and other symbols. is syntactically Example: inta, b, c; FTSM : : TK 1914 20112012 incorrect. 44
COMMAS AND SEMICOLONS • Commas separate items in a list. Example: int a, b, c; • All C++ statements end with a semicolon. Example: area = length * width; • Semicolon is also called a statement terminator. FTSM : : TK 1914 20112012 45
DOCUMENTATION • Programs are easier to read and maintain if they are well-documented. • Comments can be used to document code – Single line comments begin with // anywhere in the line – Multiple line comments are enclosed between /* and */ FTSM : : TK 1914 20112012 46
DOCUMENTATION • Avoid putting in useless comments such as shown below: int main() { … min = elapsed_time / 60; sec = elapsed_time % 60; hr = min / 60; min = min % 60; … } // assign elapsed_time / 60 to min // assign elapsed_time % 60 to sec // assign min / 60 to hr // assign min % 60 to min FTSM : : TK 1914 20112012 47
DOCUMENTATION • The program comments below are more useful: int main() { … // Convert elapsed_time to min: sec min = elapsed_time / 60; sec = elapsed_time % 60; // Convert min: sec to hr: min: sec hr = min / 60; min = min % 60; … } FTSM : : TK 1914 20112012 48
DOCUMENTATION • Name identifiers with meaningful names. • For example, which of the statements below is more meaningful? a = l * w; area = length * width; FTSM : : TK 1914 20112012 49
FORM AND STYLE • Consider two ways of declaring variables: – Method 1 int feet, inch; double x, y; – Method 2 int a, b; double x, y; • Both are correct, however, the second is hard to read FTSM : : TK 1914 20112012 50
SYNTAX AND LOGICAL ERROR FTSM : : TK 1914 20112012 51
SYNTAX ERRORS • Syntax errors are errors in the source code which are related to the syntax of the language. • Syntax errors are detected by the compiler. An executable file will be generated by the compiler only if the source code it compiles has no syntax errors. • Syntax errors are reported by the compiler in the form of error messages. FTSM : : TK 1914 20112012 52
#include <iostream> using namespace std; int main() { cout << "This program has errors return; } Error messages displayed by the compiler FTSM : : TK 1914 20112012 53
LOGICAL ERRORS • Logical errors are errors which are related to program logic. • Normally, logical errors are not detectable by the compiler. • Logical errors are usually detected during program runtime. For example, a program producing unexpected results is an indication that it has logical errors. • It is important to remember that if the compiler does not produce any error messages, it does not mean that your program is free of logical errors. FTSM : : TK 1914 20112012 54
LOGICAL ERRORS • Possible to remove all syntax errors in a program and still not have it run • Even if it runs, it may still not do what you meant it to do • For example, 2 + 3 * 5 and (2 + 3) * 5 are both syntactically correct expressions, but have different meanings FTSM : : TK 1914 20112012 55
§ Write a program to calculate the area of the region in blue. #include <iostream> using namespace std; int main() { float radius, length, width; cout << "Enter radius, length and width: "; cin >> radius >> length >> width; cout << "Area of blue region: " << length * width 3. 14*radius; return 0; } FTSM : : TK 1914 20112012 56
Suppose we test the program with these inputs: radius: 7 length: 2 width: 3 Area of circle = 3. 14 * 7 = 153. 86 Area of rectangle = 2 * 3 = 6 This means that the rectangle is enclosed by the circle. The area of the region should not be negative. FTSM : : TK 1914 20112012 57
• The following output is generated when the program is executed with those inputs. • The program should be checked for logical errors. FTSM : : TK 1914 20112012 58
#include <iostream> using namespace std; int main() { float radius, length, width; cout << "Enter radius, length and width: "; cin >> radius >> length >> width; cout << "Area of blue region: " << length*width - 3. 14*radius; return 0; } The formula should be 3. 14*radius – length*width FTSM : : TK 1914 20112012 59
YOU SHOULD NOW KNOW… • what an algorithm is. • when an algorithm should be developed when building a computer program. • the basic steps in building a computer program to solve a problem. • what flowcharts are. • how to represent algorithms graphically using flowcharts. FTSM : : TK 1914 20112012 60
YOU SHOULD NOW KNOW… • importance of program readability – using whitespace characters – inserting comments – using meaningful names for identifiers • syntax and logical errors FTSM : : TK 1914 20112012 61
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