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Lab : Recursion Solution
Information
In-class labs are meant to introduce you to a new topic and provide some practice with that new topic.
Topics: Writing simple recursive functions
Solo work: Labs should be worked on by each individual student, though asking others for help is permitted. Do not copy code from other sources, and do not give your code to other students. Students who commit or aid in plagiarism will receive a 0% on the assignment and be reported.
Building and running: If you are using Visual Studio, make sure to run with debugging. Do not run without debugging!
Using the debugger will help you nd errors.
To prevent a program exit, use this before return 0;
cin.ignore(); cin.get();
Turn in: Once you're ready to turn in your code, prepare the les by
doing the following: (1) Make a copy of your project folder and name it
LASTNAME-FIRSTNAME-LABNAME. (Example: HOPPER-GRACE-LAB-UNIT-TESTS)
Make sure that all source les (.cpp, .hpp, and/or .h les) and the Makefile les are all present. (3) Remove all Visual Studio les - I only want the source les and Make les. (4) Zip your project folder as LASTNAME-FIRSTNAME-LABNAME.zip
Never turn in Visual Studio les!
Starter les: Download from GitHub.
Grading: Grading is based on completion, if the program functions as intended, and absense of errors. Programs that don't build will receive 0%. Besides build errors, runtime errors, logic errors, memory leaks, and ugly code will reduce your score.
Contents
1.1
About . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3
1.1.1
Setting up the project . . . . . . . . . . . . . . . . . .
3
1.2
Lab speci cations . . . . . . . . . . . . . . . . . . . . . . . . .
4
1.2.1
Function 1: CountUp . . . . . . . . . . . . . . . . . . .
4
1.2.2
Function 2: MultiplyUp . . . . . . . . . . . . . . . . .
5
1.2.3
Function 3: Factorial . . . . . . . . . . . . . . . . . . .
6
1.2.4
Function 4: CountConsonants . . . . . . . . . . . . . .
7
1.2.5
Function 5: GetFirstUppercase . . . . . . . . . . . . .
8
1.1 About
Recursion can be hard to think in terms of, especially early on. For this lab, we will step through some recursive functions, and then you will be challenged to try to design solutions for the others.
Reference the textbook, reading notes, and lectures for help.
1.1.1 Setting up the project
Download the starter zip le, LAB-RECURSION-INTRO.zip, o GitHub. This zip contains the following:
function1.hpp function2.hpp function3.hpp function4.hpp function5.hpp
program main.cpp Makefile
All of these sources belong in one project and are not separate programs. The main program has a main menu to allow the user to run one function at a time. Each of the function les contains stubs for iterative and recursive
functions.
1.2 Lab specifications
1.2.1
Function 1: CountUp
1
void
C o u n t U p _ I t e r (
int
start ,
int
end
)
2
{
3
}
4
5
void
C o u n t U p _ R e c (
int
start ,
int
end
)
6
{
7
}
For this rst set of functions, you will write each of these so that they display the numbers between start and end (inclusive), going up by 1 each time. The output will look like this:
CountUp , It er at iv e :
1
2
3
4
5
6
7
8
9
10
CountUp , Re cu rs iv e :
1
2
3
4
5
6
7
8
9
10
Iterative version
The iterative version is pretty easy - write a for-loop and display each number.
Recursive version
For the recursive version, follow these steps:
Display start, plus one tab, with a cout statement.
Terminating case: If the value of start and end are the same, then return; out of the function.
Recursive case: Call CountUp Rec, passing in start+1 and end. Once you get it working, move on to the next function.
1.2.2
Function 2: MultiplyUp
1
void
M u l t i p l y U p _ I t e r (
int
start ,
int
end
)
2
{
3
}
4
5
void
M u l t i p l y U p _ R e c (
int
start ,
int
end
)
6
{
7
}
This function is similar to CountUp, except it multiplies the value each time. The output will end up looking like this:
MultiplyUp , It e ra ti ve :
2 4 16 256
MultiplyUp , Re c ur si ve :
2 4 16 256
Terminating case: Stop once start is greater than end. You can use return; to leave a function, even though its return-type is void.
Recursive case: Call the function again, passing in start start and end.
1.2.3 Function 3: Factorial
int F a c t o r i a l _ I t e r ( int n )
2 {
return -1; // p l a c e h o l d e r ;
4 }
5
6 int F a c t o r i a l _ R e c ( int n )
7 {
8 return -1; // p l a c e h o l d e r
}
For these functions, some value n is passed in. Each of these will calculate n! by computing n (n 1) (n 2) ::: 2 1. For the recursive case, we can think of the calculation recursively:
n! = n (n 1)!
and
n! = n (n 1) (n 2)!
Terminating case: End once n = 1, returning the value of n. (At this point, we don't need to go past 1 in our calculation.)
Recursive case: Multiply n by (n 1)!
How do you calculate (n 1)! ? You call Factorial Rec again, but passing in n 1.
Factorial , It er at iv e :
2!
=
2
3!
=
6
4!
=
24
5!
=
120
6!
=
720
7!
=
5040
8!
=
40320
9!
=
362880
Factorial , Re cu rs iv e :
2!
=
2
3!
=
6
4!
=
24
5!
=
120
6!
=
720
7!
=
5040
8!
=
40320
9!
=
362880
1.2.4 Function 4: CountConsonants
int C o u n t C o n s o n a n t s _ I t e r ( string text )
2 {
return -1; // p l a c e h o l d e r
4 }
5
6 int C o u n t C o n s o n a n t s _ R e c ( string text , int pos )
7 {
8 return -1; // p l a c e h o l d e r
}
For CountConsonants, it will iterate through each letter in the text pa-rameter, incrementing a counter each time it nds a consonant.
You can use the included function, bool IsConsonant( char letter ) to check each letter.
You can also treat a string as an array of chars, so accessing text[0] would give you the rst letter. You can also access the string's size with text.size(). For instance, if you wanted to display each letter from a string text, you could use:
for ( int i = 0; i < text.size(); i++ )
cout << text[i] << endl;
Terminating case: If you're at the end of the string (that is, pos = text.size()), then return 0.
Recursive case: You will have 1 if the current letter (text[pos]) is a consonant, and 0 if the current letter is not. Add this value to the consonants You will add CountConsonants Rec, passing in text and pos + 1.
GetConsonants , It er at iv e :
* C o n s o n a n t s in aeiou : 0
* C o n s o n a n t s in kittens : 5
* C o n s o n a n t s in d e v e l o p m e n t : 7
GetConsonants , Re cu rs iv e :
* C o n s o n a n t s in aeiou : 0
* C o n s o n a n t s in kittens : 5
* C o n s o n a n t s in d e v e l o p m e n t : 7
1.2.5 Function 5: GetFirstUppercase
char G e t F i r s t U p p e r c a s e _ I t e r ( string text )
2 {
return ' '; // p l a c e h o l d e r
4 }
5
6 char G e t F i r s t U p p e r c a s e _ R e c ( string text , int pos )
7 {
8 return ' '; // p l a c e h o l d e r
}
For this function, it will go through the entire text string. If it encounters an uppercase letter, it will return that letter. If the entire string is searched and no uppercase letter is found, it will return a space char: ' '.
For the recursive version, there will be two terminating cases: if you nd an uppercase letter (then return it), and if you get to the end of the string (return ' ').
The recursive case should be similar to with the previous function.
GetFirstUppercase , It er at iv e :
*
First upper - case in how are YOU ?: 'Y '
*
First upper - case in What ?: 'W '
*
First upper - case in where am I ?: 'I '
* First upper - case in no caps : ' '
GetConsonants , Re cu rs iv e :
*
First upper - case in how are YOU ?: 'Y '
*
First upper - case in What ?: 'W '
*
First upper - case in where am I ?: 'I '
*
First upper - case in no caps : ''
