0-Slot05-06-07-Basic-Logics

1. Slots 05-06-07: Lesson 3
Basic Logics: Module-C-Logic
Logic Constructs /Programming Style /Walkthroughs

2. Objectives
• How to develop a C- program? → Logic
constructs
• When I develop a C-program, what are things
that I should follow? → Programming styles
• How I can understand a program? →
Walkthroughs

3. Contents
1- Logic constructs
2- Programming Styles
3-Walkthroughs
4-Bonus – Redirect a
Program ( a technique is
used in the ACM Contest)
3

4. Review
• A variable is a name referencing to a memory
location.
• A data type defines: How the values are stored
and how the operations on those values are
performed.
• 4 primitive data types in C: int, char, float,
double
• Data stored are in binary format
• Declare a variable in C: type var [=initialValue];
• An identifier begin with a letter or ‘_’, the later
symbols can be letters, digits and ‘_’
• An user-defined identifier must not a C
keyword.
• Expression is a valid association of constants,
variables, operators and functions.
4
Basic Logics

5. Creativity in Algorithms
• Creativity has to do with both the process you invent (an algorithm) to
solve a new problem in a given context and how you implement that
• Selection:
• most commonly seen in if-statements
• The JUMP...IF command in the Human Machine Language is a form of
selection. It gives us a way to compare two things (numbers) and take
action if one thing was true.
• Iteration:
• also known as "looping“
• The JUMP command in the Human Machine Language allows us to
move to a different point in the program and start executing from
there. This allows us to re-use lines of code, and this is a form of
iteration or looping.
• Sequencing:
• Sequencing is the application of each step of an algorithm in the
order in which the statements are given.“
• The sequencing is simply implied by the fact that we number the
instructions with the intent to execute them in order.
5
Basic Logics

6. Logic Constructs
• Logic constructs: Expressions enable us to write programs
that perform creative algorithm (calculations and execute
statements) in a sequential order.
• Structured Programming
• Logic constructs:
• Sequence constructs
• Selection constructs
• Iteration constructs
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Basic Logics

7. Structured Programming
• Structure of a program code
should be organized in a manner
so that it is understandable,
testable and readily modifiable.
➔It consists of simple logical
constructs, each of which has one
entry point and one exit point.
• The beginning step for
developing a program is
DESIGN using
• pseudo-coding or
• flow charting
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Basic Logics

8. Structured Programming: Pseudo-code
• Example: Calculating the absolute value of an integer
inputted from the keyboard.
1. Prompt the user for an integer value
2. Accept an integer value from the user
and store it in x
3. If x is negative number then x = -x
4. Display x
8
Basic Logics

9. Structured Programming: Flowcharting
• A flowchart is a diagram that depicts
the “flow of control” of a program.
• Three types of symbols in this
flowchart
• rounded rectangles
• parallelograms
• a rectangle
• Terminals
• represented by rounded
rectangles
• indicate a starting or ending point
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Basic Logics

10. Structured Programming: Flow chart symbols
• Flow chart symbols Selection (Decision diamond)
• A 2-way branch. An if or another decision. The condition appears inside the diamond.
Example: x<y? Two arrows lead out of the decision. These arrows may be labeled
with Yes and No, meaning the then and else branch, respectively.
• Flow chart symbols Iteration
• Start of a repeated block. A for statement or similar. The end of the loop body connects
back to the loop symbol. How many times the loop executes depends on what is written
inside the loop symbol.
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Basic Logics

11. Sequence Constructs
• Tells the processor which statement is to
be executed next.
• the statement follows first statement
in the program.
• use a goto statement to jump
• computer programming (1950's to
early 1960's)
• A sequence is either a simple statement
or a code block.
• Simple Statements
expression ;
• Code Blocks: A code block is a set of
statements enclosed in curly braces.
{statements; }
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Basic Logics

12. Creative thinking
• Write a C program to check
whether a given number is even or
odd.
• Write a C program to check
whether a student can pass or fail
based on his/her mark
• Selection Constructs

13. Selection Constructs
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Basic Logics
• Gives a program the ability to
choose which instruction(s) to
next execute based on
conditions
• Types:
• single-selection statement (if
statement)
• double-selection statement
(if-else statement)
• multiple-selection statement
(nested if-else)
• multiple-selection statement
(switch/case)
• If the condition is a value
of char/integer

14. Selection Constructs : if statement
14
Basic Logics
• single-selection statement (if statement)
• Syntax
if (condition)
{
statements;
}
condition
evaluated
statement
true
false
• The if selection statement either
performs statements if a condition is
true or skips the statements if the
condition is false.

15. Selection Constructs: if Examples
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Basic Logics

16. Selection Constructs : if-else statement
16
Basic Logics
• double-selection statement (if-else statement)
• Syntax
if (condition)
{ statements 1;
} else
{ statements 2;
}
• The if…else selection statement
performs statements 1 if a condition is
true and performs a statements 2 if
the condition is false.
condition
statement1
true false
statement2

17. Selection Constructs: if-else Examples
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Basic Logics

18. Selection Constructs: if … else errors
The compiler can not
determine the if statement
before the else statement.
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Basic Logics

19. Selection Constructs : nested if-else statement
19
Basic Logics
• multiple-selection statement
• Syntax
if (condition 1)
{ statements;
}
else if (condition2)
{ statements;
}
else
{ statements;
}
Nested if
• Buying N T-shirts with promotion:
• N<=3: 120000$/item
• From 4th to 6th:
90000$/item
• From 7th to 10th:
85000$/item
• From 11th : 70000$/item
• Describe the expression that
will compute the paid value.
Let N: number of T-shirts bought, t: money must be paid.
if (N <=3) t = N*120000 ;
else if (N<=6) t= 3*120000 + (N-3) * 90000;
else if (N<=10)
t= 3*120000 + 3*90000 + (N-6)*85000;
else
t= 3*120000 + 3*90000 + 4*85000 + (N-10)*70000;

20. Selection Constructs: Dangling Else
• Ambiguity may arise in the case of nested if else constructs.
• The rule in C is that an else always belongs to the innermost if
available. Use { } to explicitly determine statements
20
Basic Logics

21. Exercises
• Write a C program to check whether a
given number is even or odd.
• Write a C program to accept the height
of a person in centimeter and categorize
the person according to their height.
• Write a C program to check whether a
character is an alphabet, digit or special
character.

22. Please Goto Workshop 02

23. Exercises Code

24. Selection Constructs: Operator ? :
24
Basic Logics
(condition) ? True_Value : False_Value

25. Selection Construct: The switch statement
switch (variable or expression)
{
case constant :
statement(s);
break;
case constant :
statement (s);
break;
default:
statement (s);
}
char / int
25
Basic Logics
• The switch statement evaluates an expression, then attempts to match
the result to one of several possible cases
• The match must be an exact match
• A break statement causes control to transfer to the end of the switch
statement
• If the break statement is missed, the next statements are executed
until a break is detected or all statements in the body of the switch are
executed.
• Each case is an entry of a selection
• If the break statement is missed, the next statements are executed
until a break is detected or all statements in the body of the switch are
executed.
• Each case is an entry of a selection

26. Selection Construct: The switch statement
26
Basic Logics
If input is 8, what are outputs?
a) 200000 , 2
b) 300000, 3
c) 0, 0
d) 1000000, 4
e) 1500000, 10
f) None of the others
If input is 7, what are outputs

27. Selection Construct: The switch statement
• Write a program that allows
user inputting a simple
expression containing one of
four operators +, -, *, / then
the result is printed out to
the monitor.
• Input format:
num1 operator num2,
Example: 4*5
27
Basic Logics

28. Exercises
• Write a program in C which is a Menu-
Driven Program to compute the area of
the various geometrical shape.
• Write a program in C which is a Menu-
Driven Program to perform a simple
calculation.

29. Please Goto Workshop 02

30. Exercises Code

31. Exercises Code

32. Chapter 2: Program Correctness and Efficiency 32
Syntax Errors
• Syntax errors: grammatical mistakes
in a program
• The compiler detects syntax errors
• Executable code will not be created
until you correct all of the syntax
errors
• Most frequent syntax errors are:
• Missing Parenthesis (})
• Printing the value of variable
without declaring it
• Missing semicolon

33. Creative
thinking
• Want to do some
repetitive sequence of
actions:
• print vertical line of *s
*
*
*
*
*
• Corresponding
program:
printf(“*n”);
printf(“*n”);
printf(“*n”);
printf(“*n”);
printf(“*n”);

34. Creative
thinking
• Write a program in
C to display the first
10 natural numbers.
• Corresponding
program:
printf(“1 n”);
printf(“2 n”);
printf(“3 n”);
printf(“4 n”);
printf(“5 n”);
printf(“6 n”);
printf(“7 n”);
printf(“8 n”);
printf(“9 n”);
printf(“10 n”);

35. Creative
thinking
How could you write a
program that display
4000 number?

36. Iteration (loop) Constructs
• A loop is a programming construct that executes lines of code
repeatedly while condition is met.
• Three loop constructs make it possible to iterate over code or
execute it more than once:
• for loops.
• while loops.
• do … while loops.
• Structure of a loop:
• First: Initial block.
• Second: Condition.
• Third: Task in each execution.
• Types of iteration: fixed loops, variable loops
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Basic Logics

37. Iteration (loop) Constructs
• Structure of a loop:
• First: Initial block: i=0
• Second: Condition: i<=10
• Third: Task in each execution: printf(“%d”,i); i=i+1;
• Types of iteration: fixed loops, known the number of repetition
line of code.
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Basic Logics

38. Creative
thinking
How could you write a
program that would read
in five values and display
the average?

39. Creative
thinking
• How hard would it be to change
the program to average four
thousand values?
• How hard would it be to change
the program so it could read in
the number of values to be read
and then compute the average?

40. Iteration…
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Basic Logics
• Structure of a loop:
• First: Initial block:
i=0,S=0
• Second: Condition: i<=n
• Third: Task in each
execution: S=S+i;i=i+1;
• Types of iteration: fixed
loops, known the number
of repetition line of code.

41. Iteration…
• What we need to know for a
loop
- How many time that these
lines of code need to be
executed?
• Identify a loop for an
expression:
• Left side → Initial block
• Right side → Condition to
run these lines of code
• An operation and
preparations for the next
iteration: Tasks (lines of
code) in each iteration.
41
Basic Logics
Left side
Right side
An operation

42. Iteration…
42
Basic Logics

43. Iteration: for statement
InitBlock
Condition?
Task1
Task2
yes
no
43
Basic Logics
• A for loop is used when a loop is to be executed
a known number of times
• for (InitBlock; Condition; Task2) Task1;
• for ( Init1, Init2; Condition ; Task1, Task2);
• InitBlock;
for ( ; Condition ; Task2) Task1;
• InitBlock;
for ( ; Condition ;)
{
Task1;
Task2;
}
• The InitBlock set the initial
value of the loop control
variable.
• The Condition test the value
of the loop control variable.
• The Task2 update the loop
control variable
• The Task1 might be the
repeated Tasks in some
cases
The condition will be tested
before tasks are performed.

44. Iteration for() Example
• Write a program in C to display the first 10 natural numbers.
44
Basic Logics

45. Iteration for() Example
• Write a program that will print out the
ASCII table.
ASCII code : 0 → 255
Initialize: int code =0
Condition: code <256
Task:
Print the code using 4 format: %c, %d, %o, %X
code = code +1
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Basic Logics

46. Iteration for() Example Code
46
Basic Logics

47. Iteration for() Example
• Write a program in C to display the first 10 natural numbers.
47
Basic Logics

48. Iteration for() Example
• Write a program that will calculate 1+2+3+…+n.
Accepted variable: int n
Sum 1 .. N → int sum
Algorithm
Accept n
Loop:
Initialize i=1, sum=0
Condition i<=n
Tasks: sum += i; i++;
Print out sum
48
Basic Logics

49. Exercises
• Write a program in C to display the n
terms of odd natural number and their
sum like:
1 3 5 7 ... N
• Write a program in C to display the n
terms of harmonic series and their
sum. The series is :
1 + 1/2 + 1/3 + 1/4 + 1/5 ... 1/n terms
Basic Logics 49

50. Exercises Codes
50
Basic Logics

51. Exercises
• Write a program in C to Check Whether
a Number can be perfect Numbers.
Basic Logics 51

52. Exercises(nested loop)
• nested loop: A loop placed inside another
loop.
• Write a program in C to make such a pattern like
right angle triangle with “*”.
Basic Logics 52

53. Iteration: while() statements
The condition will be tested
after tasks are performed.
/* Initializations */
while (condition)
{ statements;
}
53
Basic Logics
• If the condition is true, the
statement is executed
• Then the condition is
evaluated again, and if it is
still true, the statement is
executed again
• The statement is executed
repeatedly until the
condition becomes false
We can test multiple conditions
using logical operator inside while
loop
InitBlock
Condition?
Task1
Task2
yes
no

54. while() statements

55. Exercises Codes
Basic Logics 55

56. Iteration: do…while() statements
The condition will be tested
after tasks are performed.
/* Initializations */
do
{ statements;
}
while (condition) ;
InitBlock
Condition?
Task1
Task2
yes no
56
Basic Logics
• The statement is executed
repeatedly while the
condition becomes false

57. Computer Science: A Structured
Programming Approach Using C 57
while() vs do…while() statements
• First, the while statement evaluates expression, which must return a boolean value.
If the expression returns true, the while statement executes the statement(s) in
the while block. The while statement continues testing the expression and executing
its block until the expression returns false.
• Instead of evaluating the expression at the top of the loop, do-while evaluates the
expression at the bottom. Thus, the statements within the block associated with
a do-while are executed at least once.

58. Iteration do while()
• Write a program that will print
out the sum of integers
inputted by user. The input will
terminate if user enters the
value 0.
Nouns: inputted integer → int x,
sum of integers → int
sum
Tasks (algorithm)
Begin
sum =0
do
{ accept x;
sum += x;
}
while (x!=0);
Print out sum
End
Implement it
by yourself.
58
Basic Logics
The following program print numbers
between 1 and 100 which are multiple
of 3 using the do while loop:

59. Iteration
• Write a program that permits user entering some characters until the ENTER
key (code 10) is pressed. The program will print out the number of digits,
number of letters, number of other keys were pressed. Accept a character:
c=getchar();
Nouns:
character inputted → char c, Number of digits → int noDigits
Number of letters → noLetters, Number of other keys → noOthers
#define ENTER 10
Algorithm
Begin
noDigits = noLetters = noOthers = c= 0
printf(“Enter a string:”);
While (c!=ENTER)
{ accept c;
if ( c>=‘0’ && c <=‘9’) noDigits++;
else if ( (c>=‘a’ && c <=‘z’) || (c>=‘A’ && c <=‘Z’) ) noLetters++;
else noOthers++;
}
Print out noDigits, noLetters, noOthers
End
Implement
it by
yourself.
The while statement is
intentionally used. So,
c=0 is assigned and the
condition c!=ENTER is
evaluated to TRUE
59
Basic Logics
Input form:
abc1234fGH+-*/?(ENTER)

60. Iteration Summary
• When a loop is needed, what loop statement should be
used?
➔ All of them can be used to satisfy your requirement.
60
Basic Logics

61. Iteration: Break/ Bypass a loop
61
Basic Logics

62. Iteration Constructs: Flags
• The one entry, one exit principle is fundamental to
structured programming.
• C includes three keywords that allow jumps across
statements: goto, continue, and break. Using any of these
keywords, except for break in a switch construct, violates
the one entry, one exit principle of structured
programming.
62
Basic Logics

63. Iteration Constructs: Flags…
• To improve readability, programmers advocated:
• the use of whitespace to identify the logical structure of
the code
• the abolition of all goto statements
• the abolition of all continue statements
• the abolition of all break statements, except with switch
• A technique for avoiding jumps is called flagging. A flag is a
variable that keeps track of a true or false state.
63
Basic Logics

64. Iteration Constructs: Flags…
Use if instead of continue
64
Basic Logics

65. Iteration Constructs: Flags…
Loop infinitively
65
Basic Logics

66. Iteration Constructs: Flags…
No flag is
used.
A flag is used.
66
Basic Logics

67. Programming Styles
• Habits in programming
• A well-written program is a pleasure to read. Other
programmers can understand it without significant
effort. The coding style is consistent and clear
throughout.
• Develop your own style guide or adopt the style outlined
here or elsewhere, but adopt some style.
Recommendations on
• Naming
• Indentation
• Comments
• Magic Values
• General Guidelines
67
Basic Logics

68. Programming Styles: Naming
•Adopt names that are self-descriptive so that
comments clarifying their meaning are unnecessary
•Use names that describe identifiers completely,
avoiding cryptic names
•Prefer nouns for variable names
•Keep variable names short - studentName rather
than theNameOfAStudent
•Keep the names of indices very short - treat them as
mathematical notation
68
Basic Logics

69. Programming Styles: Indentation
•Indent the body of any construct that is embedded
within another construct. For example,
•Use in-line
opening braces or
start opening
braces on a
newline but don't
mix the two
styles.
69
Basic Logics

70. Programming Styles: Comment
•Use comments to declare what is done, rather than
describe how it is done.
•Comments introduce what follows.
•Keep them brief and avoid decoration.
70
Basic Logics

71. Programming Styles: Magic Values
•These may be mathematical constants, tax rates,
default values or names.
•To improve readability, assign symbolic names to
these magic values and refer to the symbolic names
throughout the code.
•Use the directive
#define SYMBOLIC_NAME value
71
Basic Logics

72. Programming Styles: Magic Values…
• Compiler Idiosyncracies
• Use #define to manage idiosyncracies (đặc điểm) across
platforms.
• For example, the Borland 5.5 compiler does not recognize
the long long data type. Instead, it recognizes an _int64
data type. To improve portability, #define the data type
using a symbolic name such as LONG_LONG and embed
that name throughout our code.
72
Basic Logics

73. Programming Styles: Guidelines
• Limit line length to 80 characters - both comments and
code
• Avoid global variables
• Select data types for variables wisely and carefully
• Initialize a variable when declaring it only if the initial
value is part of the semantic of the variable.
• If the initial value is part of an algorithm, use a separate
assignment statement.
• Avoid goto, continue, break except in switch.
• Avoid using the character encodings for a particular
machine.
• Use a single space or no spaces either side of an
operator.
73
Basic Logics

74. Programming Styles: Guidelines
•Use in-line opening braces or start opening braces
on a newline but don't mix the two styles.
•Initialize iteration variables in the context of the
iteration
•Avoid assignments nested inside logical expressions
•Avoid iterations with empty bodies - reserve the
body for the algorithm
•Limit the initialization and iteration clauses of a for
statement to the iteration variables
•Distribute and nest complexity
74
Basic Logics

75. Programming Styles: Guidelines
•Avoid fancy algorithms that may be efficient but are
difficult to read
•Add additional comments where code has been fine
tuned for efficient execution
•Add an extra pair of parentheses where an
assignment is also used as a condition
•Remove unreferenced variables
•Remove all commented code and debugging
statements from release and production code
75
Basic Logics

76. 3- Walkthroughs
• Understand code is a skill of programmer.
• To understand code, we should know how the code
execute.
• To know how the code execute, we should perform each
instruction.
• A walkthrough is
• a record of the changes that occur in the values of
program variables as a program executes and
• a listing of the output, if any, produced by the program.
Ways to perform a walkthrough
• Memory Map → You knew that
• Walkthrough Tables → A simpler way
76
Basic Logics

77. Walkthroughs: Demo.
77
Basic Logics

78. Walkthroughs: Demo.
int n, i, S=0;
scanf(“%d”, &n);
for (i=1; i<=n; i+=3)
if (i%2!=0 && i%3!=0) S+=i;
printf(“%d”, S);
What is the output if the input is 15?
n 15
i 1 4 7 10 13 16
S 0+1 → 1 1+7 → 8 8+13→21
S=21
78
Basic Logics

79. Walkthroughs: Demo.
int m,n, i, S=0;
scanf(“%d%d”, &n, &m);
for (i=m; i<=n; i++) S+=i;
printf(“%d”, S);
What is the output if the input are 8 12?
Test the program:
int m,n, i, S=0;
scanf(“%da%d”, &n, &m);
for (i=m; i<=n; i++) S+=i;
printf(“%d”, S);
What is the output if the input are 8a12?
Modify Input
“%d %d” 12 8
“%d%d” 12 8
“%d%d” 12
8
“%d-%d” 12-8
79
Basic Logics

80. Walkthroughs: Demo.
Study the following code:
int n=15;
int S=0;
i=1;
while (i<2*n)
{ S+= i;
i*=4;
}
Give your opinion.
a) S=21
b) S= 85
c) A syntax error
80
Basic Logics

81. i= 1
2
3
4
5
6
Extra Demo: Print star characters
Print out 1*, “n”
Print out 2*, “n”
Print out 3*, “n”
Print out 4*, “n”
Print out 5*, “n”
Print out 6*, “n”
i
Accept N;
for ( i=1; i<=N; i++)
{ for (j=1; j<=i; j++) printf(“*”);
printf (“n”);
}
N=6
*
**
***
****
*****
******
81
Basic Logics

82. Extra Demo: Multiplication Table
N=5
5x 1= 5
5x 2=10
5x 3=15
5x 4=20
5x 5=25
5x 6=30
5x 7=37
5x 8=40
5x 9=45
5x10=50
Accept n;
for ( i=1; i<=10; i++)
Print out “%dx%2d=%2dn”, n, i, n*i
82
Basic Logics

83. 4- Redirect a Program
• A characteristic is supported by the operating system and it is
used in the ACM International contest.
➔ So, pay attention to input/output formats.
83
Basic Logics

84. Diamond Pattern
• Print out the following diamond pattern
*
* * *
* * * * *
* * * * * * *
* * * * * * * * *
* * * * * * *
* * * * *
* * *
*

85. Diamond Pattern
• Sub-problem:
• print out the upper half
• print out the lower half
• Print out upper half:
• row 1: print 4 spaces, 1 star; *
• row 2: print 3 spaces, 3 stars; * * *
• row 3: print 2 spaces, 5 stars; * * * * *
• row 4: print 1 space, 7 stars; * * * * * * *
• row 5: print 0 spaces, 9 stars; * * * * * * * * *
• Print out lower half:
• row 4: print 1 space, 7 stars; * * * * * * *
• row 3: print 2 spaces, 5 stars; * * * * *
• row 2: print 3 spaces, 3 stars; * * *
• row 1: print 4 spaces, 1 star; *

86. Diamond Pattern
• Algorithm for upper half:
• row 1: print (5-row)spaces, (2*row - 1) stars; *
• row 2: print (5-row)spaces, (2*row - 1) stars; * * *
• row 3: print (5-row)spaces, (2*row - 1) stars; * * * * *
• row 4: print (5-row)spaces, (2*row - 1) stars; * * * * * * *
• row 5: print (5-row)spaces, (2*row - 1) stars; * * * * * * * * *
• Algorithm for lower half:
• row 4: print (5-row)spaces, (2*row - 1) stars; * * * * * * *
• row 3: print (5-row)spaces, (2*row - 1) stars; * * * * *
• row 2: print (5-row)spaces, (2*row - 1) stars; * * *
• row 1: print (5-row)spaces, (2*row - 1) stars; *

87. Diamond Pattern
int row, space, star;
for(row=1; row<=5; row++){ //top half
for(space=1; space<=5-row; space++)
cout << " ";
for(star=1; star<=2*row-1; star++)
cout << "*";
cout << endl ;
}
for(row=4; row>=1; row--){ //bottom half
for(space=1; space<=5-row; space++)
cout << " ";
for(star=1; star<=2*row-1; star++)
cout << "*";
cout << endl ;
}

88. Summary
• Logic constructs = Statements can be used in a program.
• 3 Basic constructs: Sequence, selection constructs (if,
if…else, ?:, switch), Iteration constructs (for/ while/ do …
while)
• Walkthrough: Code are executed by yourself, Tasks in a
walkthrough: a record of the changes that occur in the
values of program variables and listing of the output, if any,
produced by the program.
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Basic Logics