Overview:
This assignment is on C++ programming
with emphasis on functions and characters and their ASCII codes. The
problems you will see today are selection sort (again!, this tme with
functions) and cryptography using Caesar's cypher.
As you write your program please remember to pay attention to issues of style, including:
//input: n is given
//function: reads n values from the user into array a[]
void getArray(int a[], int n) {
//fill in
}
//input: array a[] of n numbers, and n are given
//function: prints the n values stored in array a[]
void printArray(int a[], int n) {
//fill in
}
//input: array a[] of n numbers and n are given; also two indices begin and end
//between 0 and n-1
//function: finds the smallest number in a[begin]...a[end]
//return value: the index of the position of the smallest element
int findSmallest(int a[], int n, int begin, int end) {
//fill in
}
//input: array a[], two indices i and j between 0 and n-1
//function: swaps a[i] with a[j]
void swap(int a[], int i, int j) {
//fill in
}
//input: array a[] of n numbers and n are given
//function: sorts a[] in increasing order
void selectionSort(int a[], int n) {
int i = 0, spos;
while (i < n) {
spos = findSmallest(a, n, i, n-1);
swap(a, i, spos);
i = i+1;
}
return;
}
The main program should look as follows:
const int size = 10;
int main() {
int x[size];
getArray(x, size);
printArray(x, size);
selectionSort(x,size);
cout << "The sorted array is: ";
printArray(x,size);
char answer = 'n';
while (answer != 'y') {
cout <<"Do you think using functions makes programming easier and more fun? (y/n)";
cin >> answer;
if (answer =='y') {
cout << "great! you can go to the next problem..:)\n";
} else {
cout << "then..look again at today's code for selection sort..";
cout << "and compare it with the code that was all in main()..\n";
}
}
return 1;
}
Take a look at the following programs char1.cpp and char2.cpp (in EXAMPLES directory on collaboration).
//char1.cpp
//The following program gives you the ascii code of a character that you type
#include < iostream.h >
int main() {
char c;
char again = 'y';
while (again == 'y') {
cout << "Type in a character and I'll tell you its ASCII code: ";
cin >> c;
cout << "you typed char=" << c << " it's ascii code is " << (int)c << endl;
cout << "again? (y/n)" << endl;
cin >> again;
}
return 1;
}
//char2.cpp
//The following program gives you the ascii conversion table for the numerical values 32-126
#include < iostream.h >
int main() {
int i = 32;
while (i <= 126) {
cout << "code=" << i << " char=" << (char)i << endl;
i = i+1;
}
return 1;
}
Before running them, try to understand what they do. Then load them in
Xcode and run them.
The most famous instances of cryptology occur in military history, beginning with Julius caesar of the Roman Empire, who developed the Caesar Cypher, and certainly including the German Enigma code cracked by the Allies during World War II (by Alan Turing, a British mathematician).
Transmitting information securely has taken a modern turn with electronic commerce on the Internet and concerns over protection of consumer credit card information and other personal data.
A Caesar cypher, also called a shift cypher,
involves shifting each character in the message to another character
some fixed distance farther along in the alphabet. Specifically, let
s be some integer between 1 and 25 that represents the
amount of the shift. Each letter in the message is encoded as the
letter that is s units farther along in the alphabet,
with the last s letters of the alphabet shifted in a
cycle to the first s letters.
For example, if s=3, then A is encoded as D, B is
encoded as E, X is encoded as A, and Z is encoded as C. Decoding a
message requires knowing s. For example, knowing that
s=3, the code word DUPB is decoded as ARMY.
Write a program that reads a text from the user and encodes all
lower case characters (leave all other characters unchanged) using
Caesar cypher with s=3, then decodes the encoded
message. The goal is to obtain the original message.
Use the following skeleton for your program (crypt.cpp from the
EXAMPLES directory on collaboration). The body of the main functions,
encode() and decode(), is missing.
// Program skeleton to solve the cryptography problem
#include < iostream.h >
//function: read characters from the user into array a[], until the user
//enters a period. Count how many characters were entered in total
//including the period, and return this value.
int getCharArray(char a[]) {
int i;
char c = ' '; //some dummy initial value
cout << "Enter a text vertically; end it with a period:" << endl;
i=0;
while (c != '.') {
cin >> c;
a[i] = c;
i = i+1;
}
return i;
}
//input: array a[] of n characters given
//function: print the array
void printCharArray(char a[], int n) {
int i = 0;
while (i < n) {
cout << a[i];
i=i+1;
}
cout << endl;
}
//input: array a[] of n characters
//function: encode the n characters of a[] using the Caesar cypher and
//write them in order into b[]. That is, translate each character to
//the one that is 3 characters beyond it in the alphabet.
void encode(char a[], int n, char b[]) {
//fill in
}
//input: array a[] of n characters (assumed encrypted with Caesar's cyper s=3)
//function: decode the n characters of a[] into b[] using the Caesar
//cypher. That is, translate each character into the one that is 3
//characters before it in the alphabet
void decode(char a[], int n, char b[]) {
//fill in
}
//input: character arrays a[] and b[] of size n
//function: return 1 if a[] and b[] are equal, that is, every
//character matches; return 0 otherwise
int areEqual(char a[], char b[], int n) {
//fill in
}
int main () {
char original[50], cypher[50], decypher[50];
int length;
//read in the text that you want to encode
length = getCharArray(original);
//print out the text
cout << "text length = " << length << endl;
cout << "This is the text that you entered: ";
printCharArray(original, length);
//encode the text
encode(original, length, cypher);
//print out the encrypted text
cout << "This is the encrypted text: ";
printCharArray(cypher, length);
//decode it
decode(cypher, length, decypher);
//print out decoded text
cout << "This is the decrypted text: ";
printCharArray(decypher, length);
//check to see of you decrypted correctly
if (areEqual(original, decypher, length) == 1) {
cout << "Great, you're done" << endl;
} else {
cout << "OOPS! The original text and the decrypted text do not match.."<< endl;
}
return 1;
}
Hint: Do you actually need to know the ASCII code of a character in order to encode it? Keep in mind that ASCII codes of characters that are consecutive in the alphabet are consecutive! Check this out:
char c = 'a'; char x = c+1; cout << x; x = c+3; cout << x;In order to test whether a character mychar is between b and d, you can test whether
(mychar >= 'b' && 'mychar <= 'd')If your solution is elegant, it will not use ASCII codes!
Extra credit: Assume the lower case characters have been
shifted with an unknown amount s. Write a decode
function that tries all possible values of s and picks
out the good one.
To submit the algorithms first rename (Xcode->File->Rename) the file main.cpp, then drag it to the Desktop, then drag it into the csci107bf04->drop-box. The names that you choose should be your loginname followed by problem number. For instance if I were to submit the file for the first problem i would rename it as ltoma1.cpp.
The drop-box has been set up such that you don't have read access (or you could copy the solutions of your colleagues), only write access. Therefore you will not be able to see whether your file has been submitted or not. Check with me in class to make sure your files got submitted.
If you work in a team submit only one file per team.
Make sure you include your name on the top line of all your .cpp programs!!