Subtracting ASCII character/values in C++ [closed] - c++

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This a function of a code I wrote that subtracts two values which are both of type character over and over again to get a text, but the result is not a text of string but symbols instead.
I checked by cout that the keyLetters and analysis have both correct values in ASCII and clear letters before converting them to int.
The lengthText is correct too.
keyLetters is a word of 5 letters.
void originalText(string analysis, string keyLetters) {
int lengthText=analysis.length();
char originText[2000];
int hold;
int k;
for (int i=0; i<lengthText; i++) {
if(i%5==0)
k=0;
hold=keyLetters[k]-analysis[i];
if (hold<=0)
hold*=-1;
originText[i]=(char)hold;
cout<<originText[i];
k++;
}
}
A screenshot of the result I get:

Answer 1

Both keyLetters and analysis consist of characters between 'a' and 'z'.
That means the difference between characters in these two can be from -25 ('a' - 'z') up to +25 ('z' - 'a').
Then you want to represent this difference using ascii characters, multiplicing by -1 the negative case. Nothing simpler:
void originalText(string analysis, string keyLetters) {
int lengthText = analysis.length();
char originText[2000];
int hold;
int k;
for (int i = 0; i < lengthText; i++) {
if (i % 5 == 0) {
k = 0;
}
hold = keyLetters[k] - analysis[i];
if (hold < 0) {
hold *= -1;
}
originText[i] = (char)hold + 'a';
cout << originText[i];
k++;
}
}
You need shift the value in range <0,25> to printable small ascii characters <'a','z'> by adding a 'a' ascii value, that is 97. The range <0,25> in ascii are just control characters.
This will result in:
The decrypted text:
oncegpmnahioethejewasalihtpegirpehmwantedhoplacallthedacandihedidnmtcareabmuhhejshudcahallinschomlherlarenhsgetangjcatherallhhetimebutihedidnmtcareabmuhhejparentifeelingiwhethejthecareangrymriadiheeaisgchabadgirplehuinohbeashejnefejeverhakecaremfevejchhingarogndcogsharhingfjoocogrlarenhstilpcogshudieiatichooltakealpthatieriogslcbestmfpucknmtheshorcdmesnohfiniihherethereismojetmihthatgirlonedaceenhtmschomlwhichiiuniveriitcactualpcbgtleolletendhosacabogtitschmolhhatihiimojecommonandidonnohknmwanyeacthatgirlofcogriewenhtognivejsitymrcollegeifihavetmsacwhenihegohopdejlikeehenshebecameeighheenceariopdsmahuniversitcthereeaiapotmfitudcforhejtodoehichihehohallcicrewgpsmshecjiedandcriedalohahnighhsfhejshecamhmmeandherkindpajentsasqedhejabmuhthereasmnforhejunitmppabpeteajsthaheairgnningouhfjomhejeyesconhinuogspchmwevejsherefgsedtmtellmrsacanyhhingiinceiheeantedtmshayalmnehhatnighthereishwasfglfilledsoathhahnighhshesleltaloneinthedarqeihhmutanconebesideihejtmeahchhejandtmtakecajeofherinhersleepingasshedidhoherlajenhsanditgdiesehenshewascoungersmthecccpehasgothejrogndshapnotfrmmnmwherebgtbecauseofareaionandthatjeaionisbecauiehhingieillcomebackholeolleafhejthecdidhheminanctimeeihhmutanceajningmralejt
As to why this doesn't give the correct text, I leave that to OP, because i don't get this method of encryption.
The whole program:
#include <iostream>
#include <string>
#include <fstream>
#include <cmath>
using namespace std;
string encryptText(string, string);
string cryptanalyzeText(string);
void originalText(string, string);
int main() {
string text, analysis;
string key;
text = "onceuponatimetherewasalittlegirlwhowantedtoplayallthedayandshedidnotcareaboutherstudyatallinschoolherparentsgetangryatherallthetimebutshedidnotcareaboutherparentsfeelingswhethertheyareangryorsadshewassuchabadgirlletusnotbeasherneverevertakecareofeverythingaroundyoustartingfromyourparentstillyoustudiesatschooltakeallthatseriouslybestoflucknothestorydoesnotfinishherethereismoretoitthatgirlonedaywenttoschoolwhichisuniversityactuallybutpeopletendtosayaboutitschoolthatitismorecommonandidonnotknowanywaythatgirlofcoursewenttouniversityorcollegeifihavetosaywhenshegotolderlikewhenshebecameeighteenyearsoldsoatuniversitytherewasalotofstudyforhertodowhichshetotallyscrewupsoshecriedandcriedalotatnightsftershecamhomeandherkindparentsaskedheraboutthereasonforherunstoppabletearsthatwasrunningoutfromhereyescontinuouslyhoweversherefusedtotellorsayanythingsinceshewantedtostayalonethatnightherwishwasfulfilledsoatthatnightshesleptaloneinthedarkwithoutanyonebesideshertowatchherandtotakecareofherinhersleepingasshedidtoherparentsandstudieswhenshewasyoungersothecyclehasgotherroundshapnotfromnowherebutbecauseofareasonandthatreasonisbecausethingswillcomebacktopeopleaftertheydidtheminanytimewithoutanywarningoralert";
analysis = "qegegrfrafkdittgiiwmurpifvcigutcahayrrtqfkspxcpelxvyidmarrdejvhippfxcmtvebawkledukydkckelxkewctqfphqtgerqpkwgqvrrgdarxhqtrplfjvxiygsytejvhippfxcmtvebawkledrrvezvjjeqnzrgeyyittgixhqarvempxvyatjedejvaaeulghmdrhgutcpefwjrofdvestgirehgiivqtkekqerveahvzedaklizirvogpucogukerfkekfdqdcogtgerqpkwtunccogukydugjeteeysoxvroemncxhmvjiruqlwlkdvwtahcycwpfxhquksrkffiszqkjizkjlhqtvxhqtvmsyqiitakkxhmvxmrxqeidmaninfvfwctqfpwtktliewemvqtjmtkctxumnccbgvgiobnvxezfkssmarfogvzxsojfslfjrxifkjqodgtsmyqeenpkusnzqkonayrryicpxhmvxmrxqwgogtjiwqpkxogpzzeduzxyattslxgxiirkyevqvfwakyyinejvkofqchednzoeijvrstgsicmoviisjkiezavereqchsackynuxvvsuvpxhqtvaaeccstahjxupawsrtgixopqnliojjlefqkelxajgrqyltsauyicdkvhazftviqfrpofckrisjkwffgiwhqerqhaovenpjvvkuputadgexsmubidtgiebawkxhqtvesapwsrtgiynevftpmdcitqciwttckaaetlrnupxsufhismtgiiyqutsnfkeyogucchayvzeduyirqhlwepvfxexnfvsmarryfjzrgekegeejvaazvvhtaukeymnfrefjrxnuiyxhqtnmstyrwfgnwmlxguwomvklafpzkhfuyisxggxaxqeiizvyidmtbaifjfytmppsnqdvwipgjledvfaafeyledcehtavroeociiorjvvizjvvsxgvtizirwstgumdfqyirbciinfurrdevlhiqunlezuyiwmupsuzivvsavyickecihmuxsttgivogpuwhmrestrtfqnayyirqdlxbqerysqqwerqcjsnmpuxhmviiaeqemsngteuegklizijaixntsmqdrgkfqgiobnveffgixhqaumdfjvqizcectuovaifjfytmppaadpzrgatrpedv";
cout<<"\n1- The original text:\n"<<text;
cout<<"\n\nEnter a key of type string: ";
key = "cream";
cout<<endl;
cout<<"The text after it has been encrypted:\n"<<encryptText(text, key)<<endl;
cout<<"\n2- An encrpted text:\n"<<analysis;
string keyLetters= cryptanalyzeText(analysis);
cout<<"\n\nThe key is: "<<keyLetters<<endl<<endl;
cout<<"The decrypted text:\n";
originalText(analysis, keyLetters);
cout<<endl<<endl;;
return 0;
}
string encryptText(string text, string key) {
int lengthText=text.length();
int lengthKey=key.length();
int count=0;
for (int i=0; i<lengthText; i++) {
text[i]=key[count];
if (count<lengthKey-1)
count++;
else
count=0;
}
return text;
}
string cryptanalyzeText(string analysis) {
string keyLetters="aaaaa";
char ch;
int i;
int lengthText=analysis.length();
for (int keyPlace=0; keyPlace<6 ; keyPlace++) {
int alphabet[26]={0};
for (i=keyPlace; i<lengthText; i=i+5) {
ch=analysis[i];
alphabet[ch - 'a']++;
}
int max=alphabet[0];
int maxPlace=0;
for (int j=1; j<26; j++) {
if(max<alphabet[j]) {
max=alphabet[j];
maxPlace=j;
}
}
keyLetters[keyPlace]=maxPlace-4;
if (keyLetters[keyPlace]<0)
keyLetters[keyPlace]+=26+97;
else
keyLetters[keyPlace]+=97;
}
return keyLetters;
}
void originalText(string analysis, string keyLetters) {
int lengthText=analysis.length();
char originText[2000];
int hold;
int k;
for (int i = 0; i < lengthText; i++) {
if (i % 5 == 0) {
k=0;
}
hold = keyLetters[k] - analysis[i];
if (hold < 0) {
hold *= -1;
}
originText[i] = (char)hold + 'a';
cout << originText[i];
k++;
}
}

Answer 2

It appeared that since the encrypted text has been generated by %26 (mod 26), the values of the letters that was larger than 26 lost its original values. So when they have been decrypted, they were generated as incorrect letters. That's why I had to return the 26 they have lost, before doing the subtraction procedure, as it will be subtracted correctly.
void originalText(string analysis, string keyLetters) {
int lengthText=analysis.length();
char originText[2000];
int hold;
int k;
for (int i = 0; i < lengthText; i++) {
if (i % 5 == 0) {
k=0;
}
hold = (analysis[i]+26)-keyLetters[k];
if (hold < 0) {
hold *= -1;
}
hold%=26;
originText[i] = (char)hold + 'a';
cout << originText[i];
k++;
}
}
The result of it: