c++ - c encrypt decrypt not working as expected -


i trying implement encode , decode of string based on page

http://www.thecrazyprogrammer.com/2016/11/caesar-cipher-c-c-encryption-decryption.html

and here code,

string encryptstring(string message){      int i, key=95828205;     char ch;     for(i = 0; message[i] != '\0'; ++i){             ch = message[i];              if(ch >= 'a' && ch <= 'z'){                 ch = ch + key;                  if(ch > 'z'){                     ch = ch - 'z' + 'a' - 1;                 }                  message[i] = ch;             }             else if(ch >= 'a' && ch <= 'z'){                 ch = ch + key;                  if(ch > 'z'){                     ch = ch - 'z' + 'a' - 1;                 }                  message[i] = ch;             }         }       printf("encrypted message: %s", message);       return message; }  string  decryptstring(string message){       int i, key=95828205;      char ch;     for(i = 0; message[i] != '\0'; ++i){             ch = message[i];              if(ch >= 'a' && ch <= 'z'){                 ch = ch - key;                  if(ch < 'a'){                     ch = ch + 'z' - 'a' + 1;                 }                  message[i] = ch;             }             else if(ch >= 'a' && ch <= 'z'){                 ch = ch - key;                  if(ch < 'a'){                     ch = ch + 'z' - 'a' + 1;                 }                  message[i] = ch;             }         }       printf("decrypted message: %s", message);      return message; }

and called function like,

string msg="test.com",msg1,msg2; msg1 = encryptstring(msg); msg2 = decryptstring(msg1);

but getting random character while decrypt data

you have defined

key=95828205;

then add character array , store array

if(ch >= 'a' && ch <= 'z'){      ch = ch + key;      message[i] = ch;      ...

and means character has overflowed , there random number.

then if try check (in encrypt)

 if(ch >= 'a' && ch <= 'z'){       ch = ch - key;

there isn't high change value in interval.

to do

you should swap these lines (first real letter , compare it)

 ch = ch - key;  if(ch >= 'a' && ch <= 'z'){       ...

and use key wont cause char overflow (e.g. 5)

edit

test after changes

input

message: test key:     5

output encrypt

yjxy

output decrypt

test

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