Sorting array of type string, with strcmp

[gilbo]

I am going round and round in circles with this and researched everywhere I'm at a wits end.

I have two strings

string amounts[i];
string names[i];

I want to sort the names alphabetically keeping each corresponding [i] value of each together.

I'm trying to use strcmp but am struggling completely with the code. I need to use pointers?

[Zhuge]

Use a normal loop swapping the values in names[] based on the results of strcmp(), but just also add another swap for the same values of amounts[].

[gilbo]

Thank you for the reply.

I know how to code the swap I have done it for a numerical sort. I do not know how to code the strcmp function correctly.

[ne555]

Create a structure that contains the related information, overload the < operator, and call std::sort

struct A{
public:
  string amount, name;
  bool operator<(const A&b) const;
}

A array[size];
std::sort( array, array+size );

[gilbo]

struct A{
            public:
            string amount, name;
            bool operator<(const A&b) const;
            };

    for(i=0;i<SIZE-1;i++)
    {
    A amounts[i];
    A names[i];
    }


    sort( names, names+SIZE );
    

This sorts the names list alphabetical, but how do i keep the amounts together with the names when printing to a file.

Alternatively is there a way to just use the regular array, its just we havn't covered structs yet.

[ne555]

but how do i keep the amounts together with the names when printing to a file.

They are together in the struct.

A array [size];
//...
//print
for( int K=0; K<size; K++)
  file << array[K].name << ' ' << array[K].amount << std::endl;

its just we havn't covered structs yet.

Maybe it is time for learn them. Do what Zhuge suggested. However then you need to implement you sort version.

[gilbo]

Thanks for the reply --> I didn't mean to sound flippant in not wanting to learn structs its just im still having trouble with arrays etc!

Here is what I have so far with notes. Sorry if I am missing something totally obvious but I am having a little trouble understanding your code. Thanks for you patience.

struct A{
            public:
            string amount, name;
            bool operator<(const A&b) const;
            } array[SIZE];



    for (int n=0; n<SIZE; n++)
    {array[n].amount=amounts[n]; // Fill the struct with the data from my arrays? Is this correct?
    array[n].name=names[n];}



   sort(array,array+SIZE); //This gives an error. Here I want to sort the NAMES ONLY and print their corresponding 'amount' together



    ofstream outfile; //Printing to file
    outfile.open ("outputalpha.txt");
    for( int K=0; K<SIZE; K++)
    outfile << array[K].amounts << ' ' << array[K].name << std::endl;

[sohguanh]

Your array is an array of struct A so you need to tell the sort function use which data member for sorting. Hence you need to provide a comparison function or functor to the sort.

http://www.cplusplus.com/reference/algorithm/sort/

Use the second version instead.

template <class RandomAccessIterator, class Compare>
void sort ( RandomAccessIterator first, RandomAccessIterator last, Compare comp );

[ne555]

for (int n=0; n<SIZE; n++){ 
    array[n].amount=amounts[n]; // Fill the struct with the data from my arrays? Is this correct?
    array[n].name=names[n];
}

The idea was to replace the two independent arrays, with the one from the struct.
However you could copy, sort the copy, and then return the values.

bool A::operator<(const A &b) const{
  return this->name < b.name;
}

But only if makes sense. (or use an external function, as sohguanh suggested)

[gilbo]

    alphabetical:

{
    for(int i=0;i<SIZE-1;i++)
    {

        for( int j = 0; j < SIZE-1; j++ )
        {
        if( names[j].compare( names[j+1] ) > 0 )
            {
            swap (amounts[j], amounts[j+1]);
            swap (names[j], names[j+1]);
            }

        }
    }

}