bubble sorting of strings

[waqas94]

Hey Guys! I have to read data from a text file, load it into an array and then bubble sort it! Here is my code:

#include <iostream>
#include <string>
#include <fstream>
using namespace std;
void Bubble_Sort(string arr[], int length);
int main()
{
    int length;
    length=10,000;
    ifstream MyFile;
    ofstream out;
    string line;
    string arr[10000];
    
    //out.open("Write.txt");
    MyFile.open("Movies.txt");
    if (MyFile.is_open())
    {
        while (!MyFile.eof())
        {
                //out << line << endl;
                for (int i=0; i<10000; i++)
                {
                    while (getline (MyFile,line,'\n'))
                    {
                      arr[i] = line;    // works perfectly alright!
                     
                    }
                }
        }
    }
    ofstream o;
    o.open("Bubble.txt");
    if (o.is_open())
    {
        cout << " file is opened " << endl;
    }
    else 
    {
        cout << " file not opened " << endl;
    }
    Bubble_Sort(arr,length);
    // writing sorted names to a file
    for (int i=0; i<10000; i++)
    {
        out << arr[i] << endl;
    }

    system("pause");
    return 0;
}

void Bubble_Sort(string arr[], int length)
{
    string temp;
    int iteration;
    int index;
    for (iteration=0; iteration<length; iteration++)
    {
        for (index=0; index<length-iteration; index++)
          {
           if (strcmp(arr[index], arr[index+1])){  // error! underlines arr
            temp = arr[index];
            arr[index] = arr[index+1];
            arr[index+1] = temp;
              }
        }
    }
}

Basically what i am trying to do is that sort the names of 10,000 movies and then write those names to a text file. It gives an error in the nested loop by underlining arr and tells that no suitable conversion function from std::string to const char* exists. Please help me out with this. Thanks in advance!!

[jimblumberg]

You don't need the C function strcmp() to compare C++ strings. The C function strcmp() works with C-strings (character strings) not std::string.

Jim

[std10093]

Why do you use strcmp for a std::string? strcmp receives char*, not strings! You have to cast if you must use strcmp, but I do not think you are obliged to do something like that.

Note also, that when the strings are equal, strcmp returns 0. strcmp - ref for more.

However std::string has overloaded operators, so for equality, you could something like this:

#include <iostream>
#include <string>
using namespace std;
 
int main() {
 
    string s1 = "Sam";
    string s2 = "Sam";
    if(s1 == s2)
        cout << "Equal strings\n";
    else
        cout << "Unequal strings\n";
    return 0;
}

[waqas94]

So which function should i use ?

[jimblumberg]

The comparison operator.

if( string1 == string2)

You have to cast if you must use strcmp,

No you would need to use the std::string.c_str() method function if you wanted to use strcmp().

Jim

[vart]

do not use eof to control loop

why do you have 3 nested loops to read a file? Use one.

length=10,000;

will not do what you think it should do...

Check this:

#include <iostream>
int main()
{
    int length;
    length=10,000;
    std::cout << length << std::endl;
    return 0;

}

Comma Operator: ,