How do I sort txt file numbers in descending order to another file

[Ray8r]

I have the F file which has these numbers:
-9
-8
-7
-6
-5
-4
-3
-2
-1
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
I have to make these numbers in a descending order and give them to the G file. What i get in the G file is :
9
8
7
6
5
4
3
2
1
1
2
3
4
5
6
7
8
9
10
11
21
31
41
51
61

Pls help me on the code how do i do this. Thank you in advance <3

#include <iostream>
#include <stdio.h>
#include <string>
#include <cstring>
#include <fstream>
#include <algorithm>


int main()
{
  int skaitli, it = 0;
  std::string rinda;
  std::ifstream F("F.txt");
  std::ofstream G;
  G.open("G.txt");

  while(std::getline(F, rinda))
  {
 std::sort(std::begin(rinda), std::end(rinda), std::greater<int>());
 try
    {
      skaitli = std::stoi(rinda);
    }
catch(std::invalid_argument& e)
    {
      std::cout << "Nav skaitlis " << it << '\n';
      continue;
    }

G << skaitli << '\n';
   it++;
}
G.close();

}

[Handy Andy]

Hello Ray8r,

I am a little short on time here. The comments in the following code should help for a start.

#include <iostream>
#include <string>
//#include <stdio.h>  // <--- Not used or needed.
//#include <cstring>  // <--- Not used or needed.

#include <fstream>
#include <algorithm>


int main()
{
    int skaitli, it{};  // <--- ALWAYS initialize all your variables.
    std::string rinda;  // <--- Does not need initialized. Empty when defined.

    std::ifstream F("F.txt");  // <--- Use a better file name than "F". Maybe "inFile".
    // <--- How do you know it is open and usable? Need to check.

    std::ofstream G;  // <--- Should do this the same as you did the "ifstream". Use a better file name than "G". Maybe "outFile".
    G.open("G.txt");
    // <--- How do you know it is open and usable? Need to check.

    while (std::getline(F, rinda))
    {
        std::sort(std::begin(rinda), std::end(rinda), std::greater<int>());  // <--- Sort after the while loop.

        try
        {
            skaitli = std::stoi(rinda);
        }
        catch (std::invalid_argument& e)
        {
            std::cout << "Nav skaitlis " << it << '\n';
            continue;
        }

        G << skaitli << '\n';

        it++;
    }

    G.close();  // <--- Not required as the dtor will close the file when the function looses scope.

    return 0;  // <--- Not required, but makes a good break point for testing.
}

This is untested at the moment. I will test it later.

For the "std::sort" look at http://www.cplusplus.com/reference/algorithm/sort/

You will need to use the 2nd format of sort for descending order.

Andy

[lastchance]

#include <iostream>
#include <fstream>
#include <algorithm>
#include <vector>
#include <iterator>

int main()
{
   std::ifstream F( "F.txt" );
   std::ofstream G( "G.txt" );
   std::vector<int> nums;
   for ( int i; F >> i; ) nums.push_back( i );
   std::sort( nums.begin(), nums.end() );
   std::copy( nums.rbegin(), nums.rend(), std::ostream_iterator<int>{ G, "\n" } );
}

[Ray8r]

Thank you <3

[keskiverto]

Note the algorithm in lastchance's program:

1. Read all values into container
2. Sort the container
3. Write values from container

(With devious "sort ascending, write reverse".)

The OP logic is quite different:

for each line in input
  read line
  reorder characters in line
  write line to output

Therefore, line k of input is always line k of output. No reordering of lines is done.

Furthermore, you read line as text, sort characters in that text, then convert to number and finally write the number.
If line has "-4275", then the text after sort is "7542-" and std::stoi returns 7542 (because trailing '-' is not "part of integer").

[seeplus]

#include <iostream>
#include <fstream>
#include <algorithm>
#include <vector>
#include <iterator>

int main()
{
	std::ifstream F("F.txt");
	std::ofstream G("G.txt");

	if (F && G) {
		std::vector<int> nums((std::istream_iterator<int>(F)), std::istream_iterator<int>());

		std::sort(nums.begin(), nums.end());
		std::copy(nums.rbegin(), nums.rend(), std::ostream_iterator<int>{ G, "\n" });
	}
}