Question

I am shuffling songs for my program but im a little confused because when I try the compiler tells me I cant compare my struct to an int. Im wondering what yall might think?

struct Songs                 //my struct
{
string title;     
string artist;
string mem;  
};

Songs *ptr;
ptr = new Songs[25];    //dynamic array

so i told u the struct and ptr well heres the function im experiencing trouble..

void shuffle (Songs song[], Songs *ptr, string title, string mem, string  artist, int num)
{

 for (int i=0; i<(num); i++) 
 {
     int r = i + (rand() % (num-i)); // Random remaining position.
     int temp = ptr[i]; ptr[i] = ptr[r]; ptr[r] = temp;  //this isnt working
 }                                                     //but its logically sound?   

 for (int c=0; c<n; c++) 
 {
     cout << ptr[c] << " ";  // Just print 
 }      
}

Answer 1

The offending code is at int temp = ptr[i]; ... ptr[r] = temp;, you’re assigning Song and int which is not possible.

Additionally, I strongly suggest using std::vector< Song > for storage. Your code is more robust and will crash less likely, plus the vector always knows the number of Songs it contains. Example

#include <vector>
...
struct Song { ... };
...
void shuffle(std::vector< Song >& mySongs, ...)
{
   /* shuffle mySongs somehow. */
   ...
}

mySongs.size() contains the number of songs, and you can access each song with mySongs[index] (or better mySongs.at(index)) as expected. Adding new songs is done by mySongs.push_back(someSong).

Now to your question: How do I shuffle my vector of songs. Well …

/* at start of program. */
srand(unsigned(time(NULL)));
...
void shuffle(std::vector< Song >& mySongs)
{
    std::random_shuffle(mySongs.begin(), mySongs.end());
}

does the trick. See here.

Writing a song to a stream can be done by defining a function like this:

std::ostream& operator << (std::ostream& osr, const Song& mySong)
{
    osr << mySong.title << ' ' << mySong.artitst << ' ' << mySong.mem;
    return osr;
}

Now you can happily do std::cout << mySong << std::endl.