introduction to ps

1. Lecture 1- Introduction and Review

2.  Identify skills and personality traits of
successful problem solving.
 Apply standard problem-solving techniques
to aid in problem solving.
 Apply problem-solving techniques to
programming activities.
 Generate potential solutions to problems.
 Formulate and successfully communicate
the solutions to problems.

3.  Types of Problems
 Problem Solving Steps
 Problem Solving Strategies
 Algorithm Design Techniques
 Review Flowcharts
 Review C Language
◦ Basics (variables, data types, expressions, I/O,
etc.).
◦ Decisions (if statement and switch statement)

4.  Problems with Algorithmic Solutions
◦ Problems that can be solved with a series of
actions
◦ Balancing checkbook, baking a cake
◦ Alphabetizing 10,000 names
 Problems with Heuristic Solutions
◦ Problem solution requiring reasoning based on
knowledge and experience, and a process of
trial and error
◦ Solutions cannot be reached through a direct
set of steps
◦ How to buy the best stock or expand the
company
◦ Difficult to evaluate the solution

5.  People are better at solving heuristic
problems
◦ Artificial intelligence is the field of computer
science that deals with heuristic problems
 Computers are better at solving complicated
calculus problems or alphabetizing 10,000
names
◦ This class deals with algorithmic solutions

6.  Identify or Define the problem
 Analyze the problem (inputs, outputs,
formulas, constants)
 Design the Solution (flowchart,
algorithm, pseudo-code)
◦ Identify alternative ways to solve the
problem
◦ Select the best way to solve the problem
from the list of alternative solutions
◦ List instructions that enable you to solve
the problem using selected solution
 Implement (program code)
 Evaluate

8. 1. Problem: Your boss wants you to convert a
list of miles to kilometers. Since you like
programming, so you decide to write a
program to do the job.
2. Analysis
• We need to get miles as input
• We need to output kilometers
• We know 1 mile = 1.609 kilometers
3. Design
1. Get distance in miles
2. Convert to kilometers
3. Display kilometers
8

9. 9

10.  We need to read it till we understand
every detail
 We need to dissect the problem into its
component parts (e.g. problems and
sub-problems)
 We need to remove any ambiguity, extra
information
 We need to determine our knowns and
our unknowns
 We need to be aware of any assumptions
we are making.

13.  Brute-force
 Divide and Conquer
 Greedy

14.  Brute-Force:
◦ Try all possibilities
 Divide and Conquer:
1. Divide: Break the given problem into sub problems
of same type.
2. Conquer: Recursively solve these sub problems
3. Combine: Appropriately combine the answers
Merge Sort is also a sorting algorithm. The algorithm
divides the array in two halves, recursively sorts them and
finally merges the two sorted halves.

15.  Greedy:
◦ Find the local optimal step at each stage.
◦ Not necessarily globally optimal.
◦ Example:
◦ With a goal of reaching the largest-sum, at each step, the
greedy algorithm will choose what appears to be the optimal
immediate choice, so it will choose 12 instead of 3 at the
second step, and will not reach the best solution, which
contains 99.

23. 23
Function Header
Function Body

24. ◦ An identifier must consist only of letters, digits,
and underscores.
◦ An identifier cannot begin with a digit.
◦ A C reserved word cannot be used as an
identifier.
◦ A standard identifier should not be redefined.
◦ C compilers are case sensitive. (Rate, rate and
RATE are viewed as different identifiers)
 Valid identifiers: letter1, inches,
KM_PER_MILE
 Invalid identifiers: 1letter,
Happy*trout,return
2
4

25. 25

26. SYNTAX
Examples :
26
printf( format string , print list ) ;
Printf(format string);
printf("That equals %f kilometers. n", kms);
printf("enter the distance in miles> ");
printf( "Hello, World?n");
Place holder
Escape sequence

27. 27

28. SYNTAX
Examples :
28
scanf( format string , input list ) ;
scanf("%lf", &miles);
Place holder
Ampersand

29. 29

30.  Write a program to ask the user for the
width and length of a piece of land and
then tell him how many orange trees he
can grow on it. Given that each orange
tree requires 4 m2.
30

31. #include <stdio.h>
# define one_tree_space 4
int main()
{
int length,width, area, no_of_tree;
printf("Enter length of the land> ");
scanf("%d", &length);
printf("Enter width of the land> ");
scanf("%d", &width);
area = length * width;
no_of_tree = area / one_tree_space;
printf("The available number of trees is %d
treesn", no_of_tree);
return(0);
}
31
Programming Examples

32. • the result of the division operator depends
on the type of its operands
• if one or both operands has a floating point
type, the result is a floating point type.
Otherwise, the result is an integer type
• Examples
11 / 4 has value 2
11.0 / 4.0 has value 2.75
11 / 4.0 has value 2.75
15 / 3 has value 5
16 / 3 has value 5
32

33. • the modulus operator % can only be used
with integer type operands and always has an
integer type result
• its result is the integer type remainder of an
integer division
EXAMPLE
3 % 5 = 3 5 % 3 = 2 4 % 5 = 4 5 % 4 = 1
5 % 5 = 0 6 % 5 = 1 7 % 5 = 2 8 % 5 = 3
15 % 6 = 3 15 % 5 = 0
33

34.  Most conditions that we use to perform
comparisons will have one of these forms:
◦ variable relational-operator variable e.g. a < b
◦ variable relational-operator constant e.g. a > 3
◦ variable equality-operator variable e.g. a = = b
◦ variable equality-operator constant e.g. a != 10
34

35. Operator Meaning Type
< less than relational
> greater than relational
<= less than or equal to relational
>= greater than or equal to relational
== equal to equality
!= not equal to equality
35

36.  logical expressions - expressions that use
conditional statements and logical operators.
◦ && (and)
 A && B is true if and only if both A and B are true
◦ || (or)
 A || B is true if either A or B are true
◦ ! (not)
 !(condition) is true if condition is false, and false if
condition is true
 This is called the logical complement or negation
 Example
◦ (salary < 1000) || (dependents > 5)
◦ (temperature > 30.0) && (humidity > 90)
◦ !(temperature > 90.0)
36

37. if ( Expression )
StatementA
else
StatementB
NOTE: StatementA and StatementB each
can be a single statement, a null
statement, or a block.
3
7

38. Write a program to calculate the total price of
a certain purchase. There is a discount and
shipping cost:
The discount rate is 25% and the shipping is
10.00 if purchase is over 100.00.
Otherwise, The discount rate is 15% and the
shipping is 5.00 pounds.
3
8

39. if ( purchase > 100.00 )
{
discountRate = .25 ;
shipCost = 10.00 ;
}
else
{
discountRate = .15 ;
shipCost = 5.00 ;
}
totalBill = purchase * (1.0 - discountRate) + shipCost
;

40.  Used to select one of several alternatives
 BASED on the value of a single variable.
 This variable may be an int or a char but NOT
a float ( or double).
4
0

41. char grade ;
printf("Enter your letter grade: ");
scanf("%c", &grade);
switch ( grade )
{
case 'A' : printf(" Excellent Job");
break;
case 'B' : printf ( " Very Good ");
break;
case 'C' : printf(" Not bad ");
break;
case 'F' : printf("Failing");
break;
default : printf(" Wrong Input ");
}
4
1

42. Write a program to ask the user for the
brightness of a light bulb (in Watts), and print
out the expected lifetime:
Brightness Lifetime in hours
25 2500
40, 60 1000
75, 100 750
otherwise 0

43. int bright ;
printf("Enter the bulb brightness: ");
scanf("%d", &bright);
switch ( bright )
{
case 25 : printf(" Expected Lifetime is 2500 hours");
break;
case 40 :
case 60 : printf ( "Expected Lifetime is 1000 hours ");
break;
case 75 :
case 100 : printf("Expected Lifetime is 750 hours ");
break;
default : printf("Wrong Input ");
}