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Encrypting - Decrypting (STRING)

Started by TPPROG Mar 5, 2008 at 5:41 PM 5 replies 750+ views

Original Post

Mar 5, 2008 at 5:41 PM

Hey I'm quite new to this site and programming itself. I was wondering if anyone could help me fix this problem. Basically user inputs a string of characters and it encrypts it by moving each character up 3 in the alphabet. The current program spits aload of symbols after it encrypts and I don't know why. Appreciate if anyone can help. #include "stdafx.h" #include #include using namespace std; int main () { string str; char encrypt[40]; int i = 0; int offset; int choice; cout << "Enter a '1' to encrypt a message and a '2' to decrypt a message.\n"; cin >> choice; cout << "What message would you like to encrypt/decrypt?\n"; cin >> str; cout << "What do you want your offset number to be?\n"; cin >> offset; for(int i = 0; i < str.length(); i++) { encrypt = str.at(i); } if (choice = 1) { while(i = int(encrypt) + offset; i++; } } else (choice =2); { while(i = int(encrypt) - offset; i++; } } cout << encrypt <

chairthrower

Mar 5, 2008 at 6:02 PM

else (choice =2); // <-- there is a stray semicolon here

also the encrypt array is never terminated with a NULL to indicate the end of the string

Pzc

Mar 5, 2008 at 6:06 PM

There's a few problems with the code as it is.

if(choice=1) and if(choice=2) assigns the value 1 and 2 to choice, to compare you need two of them = ( it's if( choice == 1) and if(choice==2) )

your else(choice=2) should be else if(choice==2) (also note that you've got a ; too much, on the else-line)

And then finally to your question: you need to null-terminate the string, easiest way to do that would be to add

encrypt[str.length()] = '\0';

after your for-loop that copies the string.

I think that's all =)

TPPROG

Author

TPPROG

Mar 5, 2008 at 6:20 PM

Thank you very much, that seemed to fix my problem.

How would I go about on trying to encrypt a few words at the same time? at the moment it just encrypts the one word. But if you type several words it goes all funny.

streamer

Mar 5, 2008 at 7:35 PM

first of all, there are some possible problems with your code. What if your string is more than 40 chars long? You will get buffer overrun in:

for(int i = 0; i < str.length(); i++){encrypt = str.at(i);}

also after for loop you need to set it to zero again, for encoding/decoding (at least in VS2005)

You can change the code like this to get rid of that problem (and simplify the code):

#include "stdafx.h"#include <iostream>#include <string>using namespace std;int main (){string str;int i = 0;int offset;int choice;cout << "Enter a '1' to encrypt a message and a '2' to decrypt a message.\n";cin >> choice;cout << "What message would you like to encrypt/decrypt?\n";cin >> str;cout << "What do you want your offset number to be?\n";cin >> offset;if(choice == 2) offset = -offset; do{  str.at(i) = (char)(str.at(i)+offset);}while(++i<str.length());cout << str <<endl;return 0;}

swiftcoder

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2,296

swiftcoder

Mar 5, 2008 at 7:53 PM

Quote:
Original post by TPPROG
How would I go about on trying to encrypt a few words at the same time? at the moment it just encrypts the one word. But if you type several words it goes all funny.

Reading a std::string like that only reads up to the next whitespace, i.e. a single word. Instead you want to use the free function getline(), which reads until it encounters the terminating character ('\n' by default):

std::string str;std::getline(str);

Zahlman

257

Zahlman

Mar 6, 2008 at 12:28 PM

Quote:
Original post by swiftcoder
Quote:
Original post by TPPROG
How would I go about on trying to encrypt a few words at the same time? at the moment it just encrypts the one word. But if you type several words it goes all funny.

Reading a std::string like that only reads up to the next whitespace, i.e. a single word. Instead you want to use the free function getline(), which reads until it encounters the terminating character ('\n' by default):
std::string str;std::getline(str);

Just in case the poor guy doesn't have any initiative for looking up documentation, std::getline needs at least two parameters - the stream to read from, and the string to read into. Thus, 'std::getline(std::cin, str)'.

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