takes a string str as input and prints out the the lower-case letters in str in reversed order.

[closed account 4wbR92yv]

Having difficulty with recursion. Reversing a string and only printing the lower case letters.
Hi all, I'm really struggling with recursion and can't figure out how to reverse a string when I'm not given a defined length. For example, if I had a defined length, then I can swap the last letter of the string with the first and keep calling until the length is 1 or 0. In my case, I have to do the same thing but without a defined length, which basically means I need to go through the string until I find the terminating character "\0". Now I can use a while loop and calculate the amount it takes to get there, but I think that size is constantly changing when the function is called again, and I can't wrap my head around it.

Here's what I have so far.

reversed_letters(const char *str)
{
if(*(str) == '\0')
{
}
else
{
//want to print only the lower case letters
//and swap them in reverse
if(*str >= 'a' && *str <= 'z')
{
reversed_letters(str + 1);
}
//Want to just skip the index in array
else
{

}
}
}

[JLBorges]

#include <iostream>
#include <cctype>

// get a pointer to the last character of the string
const char* ptr_last_char( const char* cstr )
{
    // empty string, return nullptr
    if( cstr == nullptr || cstr[0] == 0 ) return nullptr ;

    // get to the null character at the end of the string
    const char* ptr = cstr ;
    while( *ptr != 0 ) ++ptr ;

    return ptr-1 ; // return pointer to character just before the null character
}

void print_lowercase_reverse( const char* cstr )
{
    const char* ptr = ptr_last_char(cstr) ;
    if( ptr != nullptr )
    {
        while( ptr >= cstr ) // for each character up to the first character
        {
            // if this character is a lower case character, print it out
            if( std::islower( (unsigned char)*ptr ) ) std::cout << *ptr ;
            --ptr ; // get to the next character in reverse direction
        }
        std::cout << '\n' ; // finally, print a new line
    }
}

void print_lowercase_reverse_recursive( const char* first, const char* last )
{
    // if the last character is a lower case character, print it out
    if( std::islower( (unsigned char)*last ) ) std::cout << *last ;

    if( first == last ) std::cout << '\n' ; // reached the end, print a new line
    // otherwise, repeat for the next character in reverse direction
    else print_lowercase_reverse_recursive( first, last-1 ) ;
}

void print_lowercase_reverse_2( const char* cstr )
{
    const char* last = ptr_last_char(cstr) ;
    if( last != nullptr ) print_lowercase_reverse_recursive( cstr, last ) ;
}

int main()
{
    const char cstr[] = "AbCd efGHijKL MNOpqrSTUvwxYZ!" ;
    print_lowercase_reverse(cstr) ;
    print_lowercase_reverse_2(cstr) ;
}

http://coliru.stacked-crooked.com/a/f7e1e36881c81d73

[lastchance]

#include <iostream>
#include <cctype>
using namespace std;

void reverseLower( const char *c )
{
   if ( *c )
   {
      reverseLower( c + 1 );
      if ( islower( *c ) ) cout << *c;
   }
}

int main()
{
   char str[] = "AbCdEfGh";
   reverseLower( str );
}