Unknown character at the end of string

Question

This is a practice problem from hackerrank: https://www.hackerrank.com/challenges/caesar-cipher-1 . My output matches with the expected output of the program but there is an unknown character at the end of output string.Can someone please tell me how does the unknown character occur at the end of string. Here is my code :

#include <iostream>
#include <string>
#include<cstdio>
using std::cin;
using std::string;
using std::cout;
using std::endl;

int main()
{
    int k,n;
    string text;
    cin>>n;
    cin>>text;
    cin>>k;

    for (int i = 0; i <n; i++)
    { 
        if(text[i] != '\0') //check if the character is null
        {
            if(isalpha(text[i])) //check if the character is alphabet
            {
                int d=(int)text[i] ; //obtain the ascii value
                int t=d+k;           //obtain the encrypted value
                if(t>122)            //if the encrypted value of character is greater than 122
                {
                    int extra=t-122;
                    int letter=97 +(extra-1);
                    string ans= string()+char(letter);
                    cout<<ans;
                }

                string ans= string()+char(t); //print the encrypted character
                cout<<ans;
             }
             else              //if the character is not string, then print it just like that
            {
                 cout<<text[i];
             }
        }
    }
}

Sample Output: qmhhpi-Syxd

My Output: qmhhpi-Syxd~

Answer 1

There are few bugs in your code:

1. In if(t>122) , you are checking if the encrypted character ( by Caesar cypher) has value greater than 122( ASCII for Z). But what if its value was originally in the range AZ and then key was added.
   Thus, these two lines are not correct.
   int extra=t-122; int letter=97 +(extra-1);
2. Your code is incoherent. As in if you are already given the length of the string as n , then why are you using if(text[i] != '\\0') .
   Also, why use
   string ans= string()+char(t); cout<<ans; .
   As pointed out by @chris , these two lines could simply be cout << char(t);
3. Since K can vary between [0,100] , it's better to take its MOD with 26. You can check the correct code here: Ideone link

Answer 2

The problem is that there are two outputs of string ans in the loop. So when the current letter is 'z' (the last letter of your input string) then at first the if statement is executed that prints letter 'd' and then the statmenets

string ans= string()+char(t); //print the encrypted character
cout<<ans;

are also executed that output the initial value of t.

int t=d+k;

You should use if-else statement.

Take into account that the code is unsafe very redundant and uses magic numbers like for example 122 that make it unclear.

You should include header <cctype> because you are using function isalpha declared in this header.

#include <cctype>

Header <cstdio> should be removed because none declaration is used from this header.

To output a character there is no need to create an object of type std::string . For example instead of these statements

string ans= string()+char(t); //print the encrypted character
cout<<ans;

you could just write

cout << char( t );