CS1010: Programming Methodology http://www.comp.nus.edu.sg/~cs1010/

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

 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

 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?
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CS1010 (AY2013/4 Semester 1) Recess Extra Class - 6

 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

 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.
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 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: 10-15 minutes
 Sample runs:
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: 50
There are 16 multiples of 5 or 7 in [1,50].
CS1010 (AY2013/4 Semester 1) Recess Extra Class - 9

 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 = 1 + 2 + 3
 8 is not a perfect number, because 8

1 + 2 + 4
 100 is not a perfect number, because 100

1 + 2 + 4 + 5 + 10 + 20
+ 25 + 50
 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

 Time limit: 20-25 minutes
 Sample run:
Enter number: 6
6 is a perfect number.
Enter number: 8
8 is a not perfect number.
Enter number: 100
100 is not a perfect number.
Enter number: 0
CS1010 (AY2013/4 Semester 1) Recess Extra Class - 11

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:
20-25 minutes
 Sample runs:
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: 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.
Recess Extra Class - 13 CS1010 (AY2013/4 Semester 1)

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