c++ caesar cipher program executes wrong character - c++

Question

Here is what I get when I try to encrypt "This is a test sentence!": "Ymnxp���p�����t�������"
I have tested my encryption part before and it worked fine.
Can anyone please tell me what did I do wrong here?
#include <iostream>
#include <string>
#include <fstream>
#include <stdlib.h>
#include <stdio.h>
#include "unistd.h"
using namespace std;
void displayUsage(){
// Displays how to use this program
// TODO
cout << "Instruction: \n use -r to give rotation number \n use -f to give file name" <<endl;
}
int main(int argc, char **argv){
string text;
char* input_file_name;
int rotation;
bool have_rotation = false;
bool have_input_file_name = false;
// process command-line arguement
int opt = 0;
extern char *optarg;
static const char* opt_string = "r:f:";
opt = getopt( argc, argv, opt_string);
while(opt != -1) // While there are parameters to parse, do so
{
switch(opt)
{
case 'r':
have_rotation = true;
rotation = atoi(optarg);
break;
case 'f':
have_input_file_name = true;
input_file_name = optarg;
break;
default:
displayUsage();
return 1;
}
opt = getopt( argc, argv, opt_string); // Pull the next parameter, or 0 if none.
}
if(!have_rotation)
{
displayUsage();
return 0;
}
if(have_rotation)
{
if(have_input_file_name)
{
ifstream file(input_file_name);
string text2, temp;
while(!file.eof())
{
getline(file, temp);
text2 += temp;
text2 += "\n";
}
text = text2[text2.size()-2];
}
else
{
cout <<"Enter text:"<<endl;
cin >> text;
}
}
char cipher[text.size()];
for(int i=0; i<text.size(); i++)
{
cipher[i] = text[i];
if(islower(cipher[i]))
{
cipher[i] = (cipher[i] - 'a' + rotation)%26 + 'a';
}
else if(isupper(cipher[i]))
{
cipher[i] = (cipher[i] - 'A' + rotation)%26 + 'A';
}
}
cout <<cipher<<endl;
return 0;
}

Answer 1

I guess the error is because you did not terminate your cipher array with a '\0'.
The printing function will process characters from an array (and possibly beyond) until it finds a '\0' character.
Your array should be one bigger to account for this terminating character.
Or get rid of the char array and use std::string.

Answer 2

I can get my code run if I type the sentence manually. It doesn't printout anything if I input a text file.
#include <iostream>
#include <string>
#include <fstream>
#include <stdlib.h>
#include <stdio.h>
#include "unistd.h"
using namespace std;
void displayUsage(){
// Displays how to use this program
// TODO
cout << "Instruction: \n use -r to give rotation number \n use -f to give file name" <<endl;
}
char caesar(char c, int r)
{
if(isalpha(c))
{
if(islower(c))
{
c = (((c-97)+r)%26)+97; // 97 is a value of 'a'
}
else if(isupper(c))
{
c = (((c-65)+r)%26)+65; // 65 is a value of 'A'
}
}
return c;
}
int main(int argc, char **argv){
string text;
char* input_file_name;
int rotation;
bool have_rotation = false;
bool have_input_file_name = false;
// process command-line arguement
int opt = 0;
extern char *optarg;
static const char* opt_string = "r:f:";
opt = getopt( argc, argv, opt_string);
while(opt != -1) // While there are parameters to parse, do so
{
switch(opt)
{
case 'r':
have_rotation = true;
rotation = atoi(optarg);
break;
case 'f':
have_input_file_name = true;
input_file_name = optarg;
break;
default:
displayUsage();
return 1;
}
opt = getopt( argc, argv, opt_string); // Pull the next parameter, or 0 if none.
}
if(!have_rotation)
{
displayUsage();
return 0;
}
if(have_rotation)
{
if(have_input_file_name)
{
ifstream file(input_file_name);
string text2, temp;
while(!file.eof())
{
getline(file, temp);
text2 += temp + "\n";
}
text = text2[text2.size()-2];
}
else
{
cout <<"Enter text:"<<endl;
getline(cin, text);
}
}
string output = "";
for(int i = 0; i < text.size(); i++)
{
output += caesar(text[i],rotation);
}
cout<<output<<endl;
return 0;
}