cpp/classes/combolock Source

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Description
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Create a 'combination lock' which has a <tt>string</tt> password that you can change,
which you can lock and unlock. It should have this API:
<ul>
<style>li {margin-bottom: 9pt;} </style>
<li><tt>
// construct new lock with this initial password, initially unlocked<br>
CombinationLock(string initpass)
</tt>
<li><tt>// is this lock currently locked?<br>bool isLocked()</tt>
<li><tt>// if current password equals attempt, unlock (no effect if already unlocked)<br>
void tryUnlock(string attempt)</tt>
<li><tt>// make this lock become locked (no effect if already locked)<br>void lock()</tt>
<li><tt>// if locked, print "ERROR: LOCKED" else change password to newpass<br>
void changePassword(string newpass)</tt>
</ul>

<i>Note: in practice, passwords are not stored directly, but only as <a href="http://en.wikipedia.org/wiki/Cryptographic_hash_function#Password_verification">hashes</a>.
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Remarks
Comments, history, license, etc.

Originally by Mark Redekopp (redekopp@usc.edu) and Dave Pritchard (daveagp@gmail.com)

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Engine
Choices
json list of string, bool pairs
e.g. [["good", true], ["bad", false]]

Correct answer
Template / Reference solution

Template / Reference solution

#include <iostream>
#include <string>
using namespace std;
\[
class CombinationLock {
public:
CombinationLock(string initpass);
void tryUnlock(string attempt);
bool isLocked();
void lock();
void changePassword(string newpass);
private:
bool locked; // is it locked right now?
string password; // current password
};

// construct new lock with this initial password, initially unlocked
CombinationLock::CombinationLock(string initpass) {
password = initpass; // save password
locked = false; // initially unlocked
}

// is this lock currently locked?
bool CombinationLock::isLocked() {
return locked;
}

// if current password equals attempt, unlock (no effect if already unlocked)
void CombinationLock::tryUnlock(string attempt) {
if (attempt == password)
locked = false;
}

// make this lock become locked (no effect if already locked)
void CombinationLock::lock() {
locked = true;
}

// if locked, print "ERROR: LOCKED" else change password to newpass
void CombinationLock::changePassword(string newpass) {
if (locked)
cout << "ERROR: LOCKED" << endl;
else
password = newpass;
}
]\

int main() {
cout << boolalpha;
CombinationLock myLock("0000");
cout << myLock.isLocked() << endl; // false
myLock.lock();
cout << myLock.isLocked() << endl; // true
myLock.changePassword("new-pass"); // -- ERROR: LOCKED
cout << myLock.isLocked() << endl; // true
myLock.tryUnlock("2014"); // -- shouldn't unlock, password is 0000
cout << myLock.isLocked() << endl; // true
myLock.tryUnlock("0000"); // -- unlocks!
cout << myLock.isLocked() << endl; // false
myLock.changePassword("hello123"); // -- password change OK
cout << myLock.isLocked() << endl; // false
myLock.lock();
cout << myLock.isLocked() << endl; // true
myLock.tryUnlock("0000"); // -- shouldn't unlock, wrong password now
cout << myLock.isLocked() << endl; // true
myLock.tryUnlock("hello123"); // -- unlocks!
cout << myLock.isLocked() << endl; // false
myLock.lock();
cout << myLock.isLocked() << endl; // true
return 0;
}

Java test suite
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C++ test suite
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e.g. [{"stdin":"hi", "args":["4", "5"]}, {"stdin":"noargs"}]
to just run once with no input use [{}]

[
{}
]

C++ test suite
See manual

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Property	Value
Description html markup shown to student	Create a 'combination lock' which has a <tt>string</tt> password that you can change, which you can lock and unlock. It should have this API: <ul> <style>li {margin-bottom: 9pt;} </style> <li><tt> // construct new lock with this initial password, initially unlocked<br> CombinationLock(string initpass) </tt> <li><tt>// is this lock currently locked?<br>bool isLocked()</tt> <li><tt>// if current password equals attempt, unlock (no effect if already unlocked)<br> void tryUnlock(string attempt)</tt> <li><tt>// make this lock become locked (no effect if already locked)<br>void lock()</tt> <li><tt>// if locked, print "ERROR: LOCKED" else change password to newpass<br> void changePassword(string newpass)</tt> </ul> <i>Note: in practice, passwords are not stored directly, but only as <a href="http://en.wikipedia.org/wiki/Cryptographic_hash_function#Password_verification">hashes</a>.
Epilogue html markup shown when solved	remove
Public permissions	remove
Remarks Comments, history, license, etc.	Originally by Mark Redekopp (redekopp@usc.edu) and Dave Pritchard (daveagp@gmail.com) remove
Engine
Choices json list of string, bool pairs e.g. `[["good", true], ["bad", false]]`
Correct answer
Template / Reference solution
Template / Reference solution	#include <iostream> #include <string> using namespace std; \[ class CombinationLock { public: CombinationLock(string initpass); void tryUnlock(string attempt); bool isLocked(); void lock(); void changePassword(string newpass); private: bool locked; // is it locked right now? string password; // current password }; // construct new lock with this initial password, initially unlocked CombinationLock::CombinationLock(string initpass) { password = initpass; // save password locked = false; // initially unlocked } // is this lock currently locked? bool CombinationLock::isLocked() { return locked; } // if current password equals attempt, unlock (no effect if already unlocked) void CombinationLock::tryUnlock(string attempt) { if (attempt == password) locked = false; } // make this lock become locked (no effect if already locked) void CombinationLock::lock() { locked = true; } // if locked, print "ERROR: LOCKED" else change password to newpass void CombinationLock::changePassword(string newpass) { if (locked) cout << "ERROR: LOCKED" << endl; else password = newpass; } ]\ int main() { cout << boolalpha; CombinationLock myLock("0000"); cout << myLock.isLocked() << endl; // false myLock.lock(); cout << myLock.isLocked() << endl; // true myLock.changePassword("new-pass"); // -- ERROR: LOCKED cout << myLock.isLocked() << endl; // true myLock.tryUnlock("2014"); // -- shouldn't unlock, password is 0000 cout << myLock.isLocked() << endl; // true myLock.tryUnlock("0000"); // -- unlocks! cout << myLock.isLocked() << endl; // false myLock.changePassword("hello123"); // -- password change OK cout << myLock.isLocked() << endl; // false myLock.lock(); cout << myLock.isLocked() << endl; // true myLock.tryUnlock("0000"); // -- shouldn't unlock, wrong password now cout << myLock.isLocked() << endl; // true myLock.tryUnlock("hello123"); // -- unlocks! cout << myLock.isLocked() << endl; // false myLock.lock(); cout << myLock.isLocked() << endl; // true return 0; }
Java test suite See manual
C++ test suite json list of stdin/args tests e.g. `[{"stdin":"hi", "args":["4", "5"]}, {"stdin":"noargs"}]` to just run once with no input use `[{}]`	[ {} ]
C++ test suite See manual
Forbidden substrings json list of strings e.g. `["for","while"]`	remove
Solution visibility	remove
Java imports json list of importables e.g. `["java.util.*"]`	remove
Override Java classname else defaults to websheet name	remove
Dependent on other websheets? json list of websheet names in this folder e.g. `["DataStructure"]`	remove
Is example? i.e., just a demo	remove
Add compiler flag(s) json list of flags e.g. `["-Wno-unused-variable"]`	remove
Remove default compiler flag(s) json list of flags see default_cppflags e.g. `["-Wno-write-strings"]`	remove

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