I am wondering if someone can help me trouble shoot my code. It seems to be working all properly but when I go to run it that halfway through it starts to delete my data even though I never call anything to delete it.
So for example my file goes from:
=======================
Rotated by 11 positions
=======================
Lnwypeyw lala sqz xa na lnwypeyw eb pdau sqz pwa w eppa
na pea bn znawec.
-- F. L. IyAru**
to
=======================
Rotated by 12 positions
=======================
Moxzqzx mbmb tra yb ob moxzqzx c qebv tra qxb x qqb
ob qb co aobxd.
-- G. M. JzBsv
Here is my code, I have tried going through it a few times and it all makes sense logically and have no idea while it is losing data.
#include <iostream>
#include <cctype>
#include <fstream>
using namespace std;
bool isUpper(char character){
//this will test and see if it's upper or lowercase
bool upper;
if(character>= 'A' && character <= 'Z'){
upper=true;
}
else {
upper= false;
}
return upper;
}
bool isLower(char character){
//this will test and see if it's upper or lowercase
bool lower;
if(character >= 'a' && character <= 'z'){
lower=true;
}
else {
lower= false;
}
return lower;
}
//Actual function that will rotate the character
char rotate(char character, int offset) {
char next_letter;
//Changes it if it's a lower case
if (isLower(character)) {
next_letter = character + offset;
if (next_letter > 'z'){
next_letter = (next_letter - 26);
return next_letter;
}
return next_letter;
}
else if(isUpper(character)) {
next_letter = character + offset;
if (next_letter > 'Z'){
next_letter = (next_letter - 26);
return next_letter;
}
return next_letter;
}
else {
return character;
}
}
int main() {
//variables for program
char character = 'a';
int offset = 0;
while(offset < 26){
//opens the file
ifstream fin;
fin.open("secretMessage.txt");
if(!fin.good()) {
cout << "Please check your file name!!!";
return 0;
}
//report for reading
cout << "=======================" << endl
<< "Rotated by " << offset << " positions" << endl
<< "=======================" << endl;
//Reads until it's at the end of the file
while ((! fin.eof())){
character = fin.get();
cout << rotate(character,offset);
}
//makes it run 26 times
++offset;
fin.close();
cout << endl << endl;
}
//Closes the file output.
return 0;
}
In this logic:
if (next_letter > 'z') {
next_letter = (next_letter - 26);
return next_letter;
}
you didn't think of what happens if char is signed. Test it:
assert(rotate('z', 0) == 'z');
assert(rotate('z', 1) == 'a');
assert(rotate('z', 2) == 'b');
assert(rotate('z', 3) == 'c');
assert(rotate('z', 4) == 'd');
assert(rotate('z', 5) == 'e');
Fine so far, but now:
assert(rotate('z', 6) == 'f'); // WHOOPS
Ascii 'z'+5 is 127, 'z'+6 is 128. But, z+=6 results in it being negative, so the check > 'z' fails.
bool isUpper(char ch) { return (ch >= 'A' && ch <= 'Z'); }
bool isLower(char ch) { return (ch >= 'a' && ch <= 'z'); }
// Actual function that will rotate the character
char rotate(char ch, int offset) {
if (isLower(ch)) return (ch - 'a' + offset) % 26 + 'a';
if (isUpper(ch)) return (ch - 'A' + offset) % 26 + 'A';
return ch;
}
Since you include <cctype>, you might as well use std::islower and std::isupper.
#include <cctype>
#include <fstream>
#include <iostream>
#include <algorithm>
// Actual function that will rotate the character
char rotate(char ch, int offset) {
if (std::islower(ch)) return (ch - 'a' + offset) % 26 + 'a';
if (std::isupper(ch)) return (ch - 'A' + offset) % 26 + 'A';
return ch;
}
std::string readFile(std::string const& fname) {
std::ifstream fin;
fin.exceptions(std::ios::failbit);
fin.open(fname);
return { std::istreambuf_iterator<char>(fin), {} };
}
int main() {
auto const original = readFile("main.cpp");
// makes it run 26 times
for (int offset = 0; offset < 26; ++offset) {
std::cout
<< "\n"
<< "=======================\n"
<< "Rotated by " << offset << " positions\n"
<< "=======================\n";
// Reads until it's at the end of the file
std::transform(
original.begin(), original.end(),
std::ostreambuf_iterator<char>(std::cout),
[offset](char ch) { return rotate(ch, offset); });
}
}
Actually, you can do without the complexity in main by doing in-place rotate-by-1 26 times:
auto text = readFile("main.cpp");
for (int offset = 0; offset < 26; ++offset) {
std::cout
<< "\n"
<< "=======================\n"
<< "Rotated by " << offset << " positions\n"
<< "=======================\n";
std::cout << text;
for (auto& ch : text) ch = rotate(ch, 1);
}