Creating a word shifter - c++

Question

For an assignment, I am working on creating a word shifter in C++. I have little to no experience with C++ so it has been very difficult. I think I am really close but just missing some syntax that is part of C++. Any help would be appreciated greatly.
string s = phrase;
int length = s.length();
//find length of input to create a new string
string new_phrase[length];
//create a new string that will be filled by my for loop
for (int i=0; i<length; i++)
//for loop to go through and change the letter from the original to the new and then put into a string
{
int letter = int(s[i]);
int new_phrase[i] = letter + shift;
//this is where I am coming up with an error saying that new_phrase is not initialized
if (new_phrase[i] > 122)
//make sure that it goes back to a if shifting past z
{
new_phrase[i] = new_phrase[i] - 26;
}
}
cout << new_phrase<< endl;

Answer 1

Considering your syntax,I wrote an example for you.Besides,it is conventional
to write comment before it's relevant code.
#include <iostream>
#include <string>
using namespace std;
int main()
{
//test value;
int shift = 3;
string s = "hello string";
//find length of input to create a new string
int length = s.length();
//create a new string.it's length is same as 's' and initialized with ' ';
string new_phrase(length, ' ');
for (int i=0; i<length; i++)
{
//no need to cast explicitly.It will be done implicitly.
int letter = s[i];
//It's assignment, not declaration
new_phrase[i] = letter + shift;
//'z' is equal to 126.but it's more readable
if (new_phrase[i] > 'z')
{
new_phrase[i] = new_phrase[i] - ('z' - 'a' + 1);
}
}
cout << new_phrase<< endl;
}

Answer 2

This should work.
// must be unsigned char for overflow checking to work.
char Shifter(unsigned char letter)
{
letter = letter + shift;
if (letter > 'z')
letter = letter - 26;
return letter;
}
// :
// :
string new_phrase = phrase; // mainly just allocating a string the same size.
// Step throught each char in phrase, preform Shifter on the char, then
// store the result in new_phrase.
std::transform(phrase.begin(), phrase.end(), new_phrase.begin(), Shifter);
cout << new_phrase<< endl;
UPDATE: made letter unsigned, so the overflow check works.

Answer 3

Try and investigate this code
#include <iostream>
#include <string>
#include <cctype>
void ShiftRight( std::string &s, std::string::size_type n )
{
if ( n >= 'Z' - 'A' + 1 ) return;
for ( char &c : s )
{
bool lower_case = std::islower( c );
c = std::toupper( c );
c = ( c + n -'A' ) % ('Z' -'A' + 1 ) + 'A';
if ( lower_case ) c = std::tolower( c );
}
}
int main()
{
std::string s( "ABCDEFGHIJKLMNOPQRSTUVWXYZ" );
std::cout << s << std::endl << std::endl;
for ( std::string::size_type i = 1; i <= 'Z' -'A' + 1; i++ )
{
std::str std::string s( "ABCDEFGHIJKLMNOPQRSTUVWXYZ" );
ShiftRight( s, i );
std::cout << s << std::endl;
}
return 0;
}
The output is
ABCDEFGHIJKLMNOPQRSTUVWXYZ
BCDEFGHIJKLMNOPQRSTUVWXYZA
CDEFGHIJKLMNOPQRSTUVWXYZAB
DEFGHIJKLMNOPQRSTUVWXYZABC
EFGHIJKLMNOPQRSTUVWXYZABCD
FGHIJKLMNOPQRSTUVWXYZABCDE
GHIJKLMNOPQRSTUVWXYZABCDEF
HIJKLMNOPQRSTUVWXYZABCDEFG
IJKLMNOPQRSTUVWXYZABCDEFGH
JKLMNOPQRSTUVWXYZABCDEFGHI
KLMNOPQRSTUVWXYZABCDEFGHIJ
LMNOPQRSTUVWXYZABCDEFGHIJK
MNOPQRSTUVWXYZABCDEFGHIJKL
NOPQRSTUVWXYZABCDEFGHIJKLM
OPQRSTUVWXYZABCDEFGHIJKLMN
PQRSTUVWXYZABCDEFGHIJKLMNO
QRSTUVWXYZABCDEFGHIJKLMNOP
RSTUVWXYZABCDEFGHIJKLMNOPQ
STUVWXYZABCDEFGHIJKLMNOPQR
TUVWXYZABCDEFGHIJKLMNOPQRS
UVWXYZABCDEFGHIJKLMNOPQRST
VWXYZABCDEFGHIJKLMNOPQRSTU
WXYZABCDEFGHIJKLMNOPQRSTUV
XYZABCDEFGHIJKLMNOPQRSTUVW
YZABCDEFGHIJKLMNOPQRSTUVWX
ZABCDEFGHIJKLMNOPQRSTUVWXY
ABCDEFGHIJKLMNOPQRSTUVWXYZ
As for your code then it of course is wrong. You have not to define an array of strings. And do not use magic numbers as for example 122.
Also you may include in my code a check that a next symbol is an alpha symbol.