| 4.1 |
a) until (x != 5)
b) while (x >= 7)
c) while ((x = 0) or (y <= 2))
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| 4.2 |
A while loop signals to the reader that the condition it is testing is a continue
condition. An until loop signals that the condition is an abort condition.
Even though "until XXX" can be expressed as "while not XXX" and vice-versa, the cost
of the extra syntax is paid by the benefit to the reader.
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| 4.3 |
[loop initialization]
while [condition]
...
[statement to do after every loop]
end
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| 4.4 |
Need to change line three to read: while(i >= 0)
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| 4.5 |
The program will output the following numbers, each on a separate line:
11, 2, 4, 12, 4, 16, 14, 58, 64
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| 4.6 |
This code calculates the factorial of the number inputted.
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| 4.7 |
1 5
2 4
3
4 8
5 2
6
7 17
8 0
9
10 divzero.rb:8:in `/': divided by 0 (ZeroDivisionError)
The program abnormally exits with a ZeroDivisionError, because the third time through
the loop, c is 0.
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| 4.8 |
Go to restaurant
Get seated
Order
Eat
Pay
Leave
Go to restaurant A
See host/ess
If host/ess is ready to seat you – sit
Otherwise, wait for host/ess
Order drink B
Wait C mins
Get drink B
Order food D
Wait E mins
Get food D
Eat food D
Ask for check
Receive check
Pay amount F
Leave tip G
Leave restaurant A
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| 4.9 |
The innermost loop executes 2 times, both other loops execute 5 times.
5 * 5 * 2 = 50 iterations of the inner loop.
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| 4.10 |
Infinite loops are needed for things such as menu prompts and constant input reading.
Nested loops are needed for things such as traversing a 2D array, calculating powers,
and sorting algorithms. Non-executing loops are not needed. If it is truly a never
executing loop, the code inside will never do anything, and thus there is no need for
such a loop type.
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| 4.11 |
1 balance = gets.chomp.to_i
2 interest_rate = gets.chomp.to_f / 100
3 periods = gets.chomp.to_i
4 while (periods > 0)
5 balance = balance * (1 + interest_rate)
6 periods = periods - 1
7 end
8 puts balance
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| 4.12 |
1 balance = gets.chomp.to_i
2 deposit = gets.chomp.to_i
3 interest_rate = gets.chomp.to_f / 100
4 periods = gets.chomp.to_i
5 while (periods > 0)
6 balance = balance + deposit
7 balance = balance * (1 + interest_rate)
8 periods = periods - 1
9 end
10 puts balance
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| 4.13 |
1 #!/usr/bin/ruby
2 puts "Enter a value for m"
3 m = gets.to_i
4 puts "Enter a value for n (Must be higher than m)"
5 n = gets.to_i
6 while (m >= n)
7 puts "n must be higher than m--Try Again"
8 puts "Enter a value for m"
9 m = gets.to_i
10 puts "Enter a value for n (Must be higher than m)"
11 n = gets.to_i
12 end
13 while (m < n)
14
15 if (m%2 == 0 && m%3 == 0)
16 puts m.to_s + "is divisible by 2 and 3"
17 elsif (m%2 == 0)
18 puts m.to_s + "is divisible by 2 only"
19 elsif (m%3 == 0)
20 puts m.to_s + "is divisible by 3 only"
21 end
22 m=m+1
23 end
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| 4.14 |
1 #!/usr/bin/ruby
2 puts “Enter numerator: “
3 num = gets.to_i
4 puts “Enter denominator: ”
5 den = gets.to_i
6 total = 0
7 if( den != 1 ) then
8 while ( total < num )
9 total = total + den
10 end
11 total = total – denom
12 ans = num – total
13 puts ans
14 else
15 puts 1
16 end
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| 4.15 |
1 PI = 3.14159265
2 center_x = gets.to_i
3 center_y = gets.to_i
4 radius = gets.to_i
5 total_points = gets.to_i
6
7 point = 1
8 while (point <= total_points)
9 x = Math.sin((2 * PI * point) / total_points) * radius
10 y = Math.cos((2 * PI * point) / total_points) * radius
11 puts "(" + x.to_s + ", " + y.to_s + ")"
12 point = point + 1
13 end
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| 4.16 |
The code converts a given amount of feet to a combination of feet, yards, and miles.
1 total_feet = gets.chomp.to_i
2
3 puts total_feet.to_s + " feet is"
4 miles = total_feet % 5280
5 total_feet = (total_feet - (5280 * miles))
6 yards = total_feet % 3
7 total_feet = (total_feet - (3 * yards)
8
9 puts miles.to_s + " miles"
10 puts yards.to_s + " yards"
11 puts "and " + total_feet.to_s + " feet."
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| 4.17 |
Ruby has a for loop, used for iterating over a list of objects.
for i in x...y
i is the current iteration
For the very first iteration i = x
The loop ends when i = y
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| 4.18 |
1 num = 1
2 while (num <= 10)
3 puts num
4 num = num + 1
5 end
1 num = 1
2 until (num > 10)
3 puts num
4 num = num + 1
5 end
1 for num in 1..10
2 puts num
3 end
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| 4.19 |
1 sum = 0
2 i = 2
3 until (sum > 5000)
4 sum = sum + i
5 # debugging test
6 # puts "sum ==> " + sum.to_s
7 i = i + 2
8 # debugging test
9 # puts "i ==> " + i.to_s
10 end
11 sum = sum - i
12 # Going back to the value before 5000
13 puts sum
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| 4.20 |
In both the outer loop and the inner loop the i and j values are never incremented
so the loop will not end. By adding increment values such as j = j + 1 and
i = i + 1 will fix the code.
1 i = 1
2 j = 3
3 while (i < 5)
4 a = i * 2
5 puts a
6 while (j < 10)
7 b = j + a
8 puts b
9 j = j + 1
10 end
11 i = i + 1
12 end
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| 4.21 |
1 want_to_quit = false
2 while not want_to_quit
3 input1 = gets.chomp
4 if input1 == "q"
5 want_to_quit = true
6 else
7 num1 = input1.to_i
8 num2 = gets.chomp.to_i
9 result = nil
10 until result
11 operator = gets.chomp
12 case
13 when "+" then result = num1 + num2
14 when "-" then result = num1 - num2
15 when "*" then result = num1 * num2
16 when "/" then result = num1 / num2
17 else
18 puts "invalid operator - try again"
19 end
20 end
21 puts "=" + result.to_s
22 end
23 end
When the user enters "q" for the first number, the calculator will stop running.
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| 4.22 |
1 a = 1
2 puts a
3 b = 1
4 puts b
5 i = 1
6 while (i <= 20)
7 c = a + b
8 puts c
9 a = b
10 b = c
11 i = i + 1
12 end
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| 4.23 |
1 avg = 0.0
2 sum = 0.0
3 score = 0.0
4 i = 1
5 while (i <= 5)
6 puts "Enter score #" + i.to_s
7 score = gets.to_f
8 sum= score + sum
9 i = i + 1
10 end
11 avg = sum/5
12 case
13 when (avg < 60) then puts "Grade=F"
14 when (avg >= 60 && avg < 70) then puts "Grade=D"
15 when (avg >= 70 && avg < 80) then puts "Grade=C"
16 when (avg >= 80 && avg < 90) then puts "Grade=B"
17 when (avg >= 90) then puts "Grade=A"
18 end
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| 4.24 |
The loop is different because the code within the loop will always be executed. If
the above loop was a while loop, it would never ask if you wanted to continue. This
kind of loop is useful when you need to data and modify it before checking if it in
the condition.
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