Create a new directory for this lab called lab06 by typing:
mkdir lab06Change to this directory by typing:
cd lab06
devowel.c which reads characters from its input
and writes the same characters to its output, except it does not write lower case vowels ('a', 'e','i', 'o', 'u').
Your program should stop only at the end of input.
For example:
./devowel Are you saying 'Boo' or 'Boo-Urns'? Ar y syng 'B' r 'B-Urns'? It was the best of times. It was the worst of times. It ws th bst f tms. It ws th wrst f tms.Hint: hint use
getcharto read characters don't use scanf or fgets.
Hint: use putchar to output each character.
As usual autotest is available to help you test your program.
~cs1511/bin/autotest lab06 devowel.c
devowel.c
#include <stdio.h>
int
main(void) {
int c;
// getchar returns an int which will contain either
// the ASCII code of the character read or EOF
c = getchar();
while (c != EOF) {
// print c if it is not a vowel
if (c != 'a' && c != 'e' && c != 'i' && c != 'o' && c != 'u') {
putchar(c);
}
c = getchar();
}
return 0;
}
caesar.c which reads characters from its input
and writes the characters to its output encrypted with a Caesar cipher.
A Caesar cipher shifts each letter a certain number of positions in the alphabet.
The number of positions to shift will be given to your program as a command line argument.
Characters other than letters should not be encrypted.
Your program should stop only at the end of input.
Your program should contain at least one function other than main.
For example:
./caesar 1 This life well it's slipping right through my hands Uijt mjgf xfmm ju't tmjqqjoh sjhiu uispvhi nz iboet These days turned out nothing like I had planned Uiftf ebzt uvsofe pvu opuijoh mjlf J ibe qmboofe ./caesar 10 abcdefghijklmnopqrstuvwxyz klmnopqrstuvwxyzabcdefghij ABCDEFGHIJKLMNOPQRSTUVWXYZ KLMNOPQRSTUVWXYZABCDEFGHIJ ./caesar -42 Control well it's slipping right through my hands Myxdbyv govv sd'c cvszzsxq bsqrd drbyeqr wi rkxnc These days? Droco nkic?Hint: handle upper and lower case letters separately
Hint: use %
Hint: use atoi to convert the command-line argument to an int.
As usual autotest is available to help you test your program.
~cs1511/bin/autotest lab06 caesar.c
caesar.c
#include <stdio.h>
#include <stdlib.h>
int encrypt(int character, int shift);
int
main(int argc, char *argv[]) {
int c, shift;
if (argc != 2) {
printf("Usage: %s <shift>\n", argv[0]);
return 1;
}
shift = atoi(argv[1]);
// negative shifts need to be converted to the equivalent positive shift
if (shift < 0) {
shift = 26 + (shift % 26);
}
c = getchar();
while (c != EOF) {
putchar(encrypt(c, shift));
c = getchar();
}
return 0;
}
int encrypt(int c, int shift) {
if (c >= 'A' && c <= 'Z') {
return 'A' + (c - 'A' + shift) % 26;
} else if (c >= 'a' && c <= 'z') {
return 'a' + (c - 'a' + shift) % 26;;
} else {
return c;
}
}
Naq jr'yy arire or eblnyf Vg qba'g eha va bhe oybbq Gung xvaq bs yhk whfg nva'g sbe hf Jr penir n qvssrerag xvaq bs ohmmWhat is the plain-text?
Hint:: try various shifts with caesar.c)
And we'll never be royals It don't run in our blood That kind of lux just ain't for us We crave a different kind of buzz
letter_frequency.c which reads characters from its input
until end of input.
It should then print the occurance frequency for each of the 26 letters 'a'..'z'.
The frequency should be printed as a decimal value and an absolute number in exactly the format below.
Note upper and lower case letters are counted together.
For example:
./letter_frequency Hello and goodbye. 'a' 0.066667 1 'b' 0.066667 1 'c' 0.000000 0 'd' 0.133333 2 'e' 0.133333 2 'f' 0.000000 0 'g' 0.066667 1 'h' 0.066667 1 'i' 0.000000 0 'j' 0.000000 0 'k' 0.000000 0 'l' 0.133333 2 'm' 0.000000 0 'n' 0.066667 1 'o' 0.200000 3 'p' 0.000000 0 'q' 0.000000 0 'r' 0.000000 0 's' 0.000000 0 't' 0.000000 0 'u' 0.000000 0 'v' 0.000000 0 'w' 0.000000 0 'x' 0.000000 0 'y' 0.066667 1 'z' 0.000000 0 ./letter_frequency Hey! Hey! Hey! I don't like walking around this old and empty house So hold my hand, I'll walk with you my dear 'a' 0.072289 6 'b' 0.000000 0 'c' 0.000000 0 'd' 0.084337 7 'e' 0.084337 7 'f' 0.000000 0 'g' 0.012048 1 'h' 0.096386 8 'i' 0.072289 6 'j' 0.000000 0 'k' 0.036145 3 'l' 0.084337 7 'm' 0.036145 3 'n' 0.060241 5 'o' 0.084337 7 'p' 0.012048 1 'q' 0.000000 0 'r' 0.024096 2 's' 0.036145 3 't' 0.048193 4 'u' 0.036145 3 'v' 0.000000 0 'w' 0.036145 3 'x' 0.000000 0 'y' 0.084337 7 'z' 0.000000 0Hint: use an array of counts.
As usual autotest is available to help you help test your program.
~cs1511/bin/autotest lab06 letter_frequency.c
letter_frequency.c
#include <stdio.h>
#include <stdlib.h>
int
main(int argc, char *argv[]) {
int c, n, i;
int letter_count[26] = {0}; // 1 array element for each English letter
c = getchar();
n = 0;
while (c != EOF) {
if (c >= 'A' && c <= 'Z') {
letter_count[c - 'A'] = letter_count[c - 'A'] + 1;
n = n + 1;
} else if (c >= 'a' && c <= 'z') {
letter_count[c - 'a'] = letter_count[c - 'a'] + 1;
n = n + 1;
}
c = getchar();
}
if (n > 0) {
i = 0;
while (i < 26) {
printf("'%c' %f %d\n", 'a'+i, letter_count[i]/(double)n, letter_count[i]);
i = i + 1;
}
}
return 0;
}
A Substitution cipher maps each letter to another letter.
The mapping will be given to your program as a single command line argument. This command line argument will contain 26 characters: an ordering of the letters 'a'..'z'.
Characters other than letters should not be encrypted.
Your program should stop only at the end of input.
Your program should contain at least one function other than main.
For example:
./substitution qwertyuiopasdfghjklzxcvbnm I was scared of dentists and the dark O vql leqktr gy rtfzolzl qfr zit rqka I was scared of pretty girls and starting conversations O vql leqktr gy hktzzn uoksl qfr lzqkzofu egfctklqzogfl ./substitution abcdefghijklmnopqrstuvwxyz The identity cipher!!! The identity cipher!!! ./substitution bcdefghijklmnopqrstuvwxyza The Caesar cipher is a subset of the substitution cipher! Uif Dbftbs djqifs jt b tvctfu pg uif tvctujuvujpo djqifs!As usual autotest is available to help you test your program.
~cs1511/bin/autotest lab06 substitution.c
substitution.c
#include <stdio.h>
#include <string.h>
int encrypt(int c, char mapping[]);
int
main(int argc, char *argv[]) {
int c;
if (argc != 2) {
printf("Usage: %s <mapping>\n", argv[0]);
return 1;
}
if (strlen(argv[1]) != 26) {
printf("%s: mapping must contain 26 letters\n", argv[0]);
return 1;
}
c = getchar();
while (c != EOF) {
putchar(encrypt(c, argv[1]));
c = getchar();
}
return 0;
}
int encrypt(int c, char mapping[]) {
if (c >= 'A' && c <= 'Z') {
return mapping[c - 'A'] - 'a' + 'A';
} else if (c >= 'a' && c <= 'z') {
return mapping[c - 'a'];
} else {
return c;
}
}
For example:
./decode qwertyuiopasdfghjklzxcvbnm O vql leqktr gy rtfzolzl qfr zit rqka I was scared of dentists and the dark O vql leqktr gy hktzzn uoksl qfr lzqkzofu egfctklqzogfl I was scared of pretty girls and starting conversations ./decode abcdefghijklmnopqrstuvwxyz The identity cipher!!! The identity cipher!!! ./decode bcdefghijklmnopqrstuvwxyza Uif Dbftbs djqifs jt b tvctfu pg uif tvctujuvujpo djqifs! The Caesar cipher is a subset of the substitution cipher!As usual autotest is available to help you test your program.
~cs1511/bin/autotest lab06 decode.c
decode.c
#include <stdio.h>
#include <string.h>
#define ALPHABET_SIZE 26
int encrypt(int c, char mapping[]);
int
main(int argc, char *argv[]) {
int c, i;
char mapping[ALPHABET_SIZE] = {0};
if (argc != 2) {
printf("Usage: %s <mapping>\n", argv[0]);
return 1;
}
if (strlen(argv[1]) != ALPHABET_SIZE) {
printf("%s: mapping must contain %d letters\n", argv[0], ALPHABET_SIZE);
return 1;
}
i = 0;
while (i < ALPHABET_SIZE) {
c = argv[1][i];
if (c < 'a' || c > 'z') {
printf("%s: mapping must contain only the letters 'a'..'z'\n", argv[0]);
return 1;
}
mapping[c - 'a'] = 'a' + i;
i = i + 1;
}
c = getchar();
while (c != EOF) {
putchar(encrypt(c, mapping));
c = getchar();
}
return 0;
}
int encrypt(int c, char mapping[]) {
if (c >= 'A' && c <= 'Z') {
return mapping[c - 'A'] - 'a' + 'A';
} else if (c >= 'a' && c <= 'z') {
return mapping[c - 'a'];
} else {
return c;
}
}
Ndwu fdw sojfauw xafwl dvsq Vuq vcxafaoul vsw yon Vuq fdw swlwufcwuf saqwl datd Xjf wcofaoul nouf tson Vuq nwsw kdvutaut ojs nvrl, Fviaut qappwswuf sovql Fdwu yomw, yomw nayy fwvs jl vbvsf vtvauWhat was the original text?
Hint: use letter_frequency.c on the encrypted text and compare the frequencies to English letter frequencies and then try your guesses with decode.c
When the routine bites hard And ambitions are low And the resentment rides high But emotions wont grow And were changing our ways, Taking different roads Then love, love will tear us apart again
Your program should make no assumptions about the language of the original text - don't assume its English.
Your program will be given as a command-line argument the name of a file containing a large amount of unencrypted text in the same language as the encrypted text.
Your program will be given the encrypted text on standard input. You may read it all before printing the decryption.
You may assume the encrypted text contains at most 10000 characters.
For example: /import/chopin/1/cs1511/public_html/17s1/tlb/06/unsw.txt contains 42000 characters of English text
(UNSW students on facebook)
For example, here is some English text encrypted with a Caesar cipher with an unknown shift:
Kyzj zj fli crjk xffuspv Z yrkv kf wvvc kyv cfmv svknvve lj uzv Slk zk'j fmvi Aljk yvri kyzj reu kyve Z'cc xf Pfl xrmv dv dfiv kf czmv wfi Dfiv kyre pfl'cc vmvi befnSo for example:
./crack_caesar /import/chopin/1/cs1511/public_html/17s1/tlb/06/unsw.txt Kyzj zj fli crjk xffuspv Z yrkv kf wvvc kyv cfmv svknvve lj uzv Slk zk'j fmvi Aljk yvri kyzj reu kyve Z'cc xf Pfl xrmv dv dfiv kf czmv wfi Dfiv kyre pfl'cc vmvi befn This is our last goodbye I hate to feel the love between us die But it's over Just hear this and then I'll go You gave me more to live for More than you'll ever knowHint: extract the letter frequencies from the file of unencrypted text. Use these frequencies as estimate of the probability each letter will be used. Test all possible shifts using these probabilities to see which is the most likely..
As usual autotest is available to help you test your program.
~cs1511/bin/autotest lab06 crack_caesar.c
Your program should make no assumptions about the language of the original text - don't assume its English. In other words don't hard code English properties into your program, extract the statistical properties from the sample plain text.
Your program will be given as a command-line argument the name of a file containing a large amount of unencrypted text in the same language as the encrypted text.
Your program will be given the encrypted text on standard input. You may read it all before printing the decryption.
You may assume the encrypted text contains at most 10000 characters.
For example:
./crack_substitution /import/chopin/1/cs1511/public_html/17s1/tlb/06/unsw.txt M'ka paat dra qegbu, ueta md xbb Rxu vw fxya teq Umxvetup, ogmbbmxtd, mt Oab-Xmg teq Red psvvag tmlrdp, vmu Jsbw Qrat wes xtu M qaga negakag qmbu Dra fgxzw uxwp, fmdw bmlrdp Dra qxw wes'u cbxw qmdr va bmya x frmbu Qmbb wes pdmbb beka va Qrat M'v te betlag westl xtu oaxsdmnsb? Qmbb wes pdmbb beka va Qrat M'ka led tedrmtl osd vw xfrmtl pesb? M yteq wes qmbb, M yteq wes qmbb M yteq drxd wes qmbb Qmbb wes pdmbb beka va qrat M'v te betlag oaxsdmnsb? M'ka paat dra qegbu, bmd md sc Xp vw pdxla teq Frxbbatlmtl xtlabp mt x taq xla teq Red psvvag uxwp, gefy t gebb Dra qxw wes cbxw neg va xd wesg preq Xtu xbb dra qxwp, M led de yteq Wesg cgaddw nxfa xtu abafdgmf pesb I've seen the world, done it all Had my cake now Diamonds, brilliant, in Bel-Air now Hot summer nights, mid July When you and I were forever wild The crazy days, city lights The way you'd play with me like a child Will you still love me When I'm no longer young and beautiful? Will you still love me When I've got nothing but my aching soul? I know you will, I know you will I know that you will Will you still love me when I'm no longer beautiful? I've seen the world, lit it up As my stage now Challenging angels in a new age now Hot summer days, rock n roll The way you play for me at your show And all the ways, I got to know Your pretty face and electric soulHint: you will need to look at the probabilities of sequences of 2 or perhaps 3 letters occurring or perhepas the probabilities of words.
An autotest is available to help you test your program but because this is a difficult problem it is possible very good attempts at the problem won't pass the autotests.
~cs1511/bin/autotest lab06 crack_substitution.c
lab06 directory):
give cs1511 lab06 devowel.c caesar.c letter_frequency.c substitution.c decode.c crack_caesar.c crack_substitution.cSubmit the challenge exercises only if you attempt them.
If you are working at home, you may find it more convenient to upload your work via give's web interface.
Remember the lab assessment guidelines - if you don't finish the exercises
you can finish them in your own time, submit them
by Monday 11:00am using give and ask your tutor to assess them at the start of
the following lab.
Either or both members of a programming pair can submit the work (make sure each program lists both of you as authors in the header comment).