CS1010: Programming Methodology

Extra class: 25 September 2013  Objectives:  To go over the basic concepts covered in the first 6 weeks  To give out some programming exercises to test students’ understanding of these basic concepts CS1010 (AY2013/4 Semester 1)Recess Extra Class - 2

Summary (1/2)  Week 1:  Writing algorithms (pseudo-codes)  Week 2:  Input (scanf) and output (printf)  Types (int, float, double, char, etc.) and variables  Mathematical operations (*, /, %, +, -)  About integer division  Week 3:  Top-down design  Writing functions  Using math functions  Discussion session: Writing algorithms, programming environment, using CodeCrunch CS1010 (AY2013/4 Semester 1)Recess Extra Class - 3

Summary (2/2)  Week 4:  Selection statements: ‘if’, ‘if-else’, ‘switch’  Discussion session: Inaccuracy of real numbers, initialisation of variables, redundant assignment, writing functions.  Week 5:  Repetition statements: ‘while’, ‘do-while’, ‘for’  Discussion session: Good programming practice, using selection statements, conditional operator ?:, using repetition statements.  Week 6:  Functions with address parameters  Discussion session: Repetition statements, functions with address parameters, design issues, exploration on random numbers. CS1010 (AY2013/4 Semester 1)Recess Extra Class - 4

Skills  Using vim  Pseudo-code before code  Clear logic  Can you convince yourself that your algorithm works before you start typing the program?  Simplifying the problem  If you get a complex problem, what would you do? (Reference: Week 6 Discussion Q5 Asterisks)  Incremental coding  Do you type in the whole program at one go? Or a bit at a time?  Understanding compiler’s messages  Do you know where to zoom into your program to spot the error? CS1010 (AY2013/4 Semester 1)Recess Extra Class - 5

Week 6 Discussion Q5: Asterisks  (b) CS1010 (AY2013/4 Semester 1)Recess Extra Class - 6 * *** ***** * *** ***** * *** ***** ******* ********* *********** * *** ***** ******* ********* ***********  (c) * *** ***** * *** ***** * *** ***** ******* ********* *********** * *** ***** ******* ********* ***********

Big Question  Have you been writing a lot of programs by yourself?  Target: Write 150 programs by the end of this semester  For students with no experience: 200 programs  Possible! Average about 17 programs per week over 12 weeks. Less than 3 programs a day! CS1010 (AY2013/4 Semester 1)Recess Extra Class - 7

Tracing  Another important skill: Tracing codes.  Reinforce that program execution is done step by step following the sequence, selection and repetition control structures.  Every variable should be represented by a box, and its value updated during the trace.  Manually trace the given programs in the hand-out, and write out their outputs. CS1010 (AY2013/4 Semester 1)Recess Extra Class - 8

Count multiples of 5 or 7 (Practice Ex #18)  Write a program multiples5or7.c that asks user for a positive number num, and count the number of multiples of 5 or 7 in the range [1, num].  Your program should have a function count_multiples(int)  Time limit: minutes  Sample runs: CS1010 (AY2013/4 Semester 1)Recess Extra Class - 9 Enter positive integer: 10 There are 3 multiples of 5 or 7 in [1,10]. Enter positive integer: 10 There are 3 multiples of 5 or 7 in [1,10]. Enter positive integer: 6 There is 1 multiple of 5 or 7 in [1,6]. Enter positive integer: 6 There is 1 multiple of 5 or 7 in [1,6]. Enter positive integer: 50 There are 16 multiples of 5 or 7 in [1,50]. Enter positive integer: 50 There are 16 multiples of 5 or 7 in [1,50].

Perfect numbers (Practice Ex #19) (1/2)  Definition:  A perfect number is a positive integer that is the sum of its proper positive divisors.  Examples:  6 is a perfect number, because 6 =  8 is not a perfect number, because 8   100 is not a perfect number, because 100   Write a program check_perfect.c that asks user repeatedly for a non-negative integer, and stops when the number is zero.  It should have a function is_perfect(int) that returns 1 if the parameter is a perfect number, or 0 otherwise.  For each positive integer entered, your program is to check whether it is a perfect number or not. CS1010 (AY2013/4 Semester 1)Recess Extra Class - 10

Perfect numbers (Practice Ex #19) (2/2)  Time limit: minutes  Sample run: CS1010 (AY2013/4 Semester 1)Recess Extra Class - 11 Enter number: 6 6 is a perfect number. Enter number: 8 8 is a not perfect number. Enter number: is not a perfect number. Enter number: 0 Enter number: 6 6 is a perfect number. Enter number: 8 8 is a not perfect number. Enter number: is not a perfect number. Enter number: 0

Check order of input data (Pract. Ex #20) (1/2)  Write a program check_order.c to read in a list of positive integers.  The program is to continue asking for the next positive integer as long as the integers entered so far are in increasing order.  The moment the input data are not in increasing order, or the input value is zero, the input ends.  The program should then report whether the input data are in increasing order or not.  You may assume that at least one positive integer is entered. If that is the case, we treat the list as in increasing order. CS1010 (AY2013/4 Semester 1)Recess Extra Class - 12

Check order of input data (Pract. Ex #20) (2/2)  Time limit: minutes  Sample runs: CS1010 (AY2013/4 Semester 1)Recess Extra Class - 13 Enter positive integer: 3 Enter positive integer: 0 Data are in increasing order. Enter positive integer: 3 Enter positive integer: 0 Data are in increasing order. Enter positive integer: 10 Enter positive integer: 12 Enter positive integer: 21 Enter positive integer: 0 Data are in increasing order. Enter positive integer: 10 Enter positive integer: 12 Enter positive integer: 21 Enter positive integer: 0 Data are in increasing order. Enter positive integer: 100 Enter positive integer: 102 Enter positive integer: 100 Data are not in increasing order. Enter positive integer: 100 Enter positive integer: 102 Enter positive integer: 100 Data are not in increasing order. Enter positive integer: 7 Enter positive integer: 31 Enter positive integer: 56 Enter positive integer: 56 Data are not in increasing order. Enter positive integer: 7 Enter positive integer: 31 Enter positive integer: 56 Enter positive integer: 56 Data are not in increasing order.

Reminders Revise all of the following  Textbook and lecture notes  Discussion questions  Lab exercises Write many programs! Post queries on IVLE forum and read postings by others You CAN succeed! CS1010 (AY2013/4 Semester 1)Recess Extra Class - 14

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