#include <stdio.h>
#include<conio.h>

main()
{
      int x[100][100],a,i,j;
      scanf("%d",&a);
      for( i = 0 ; i < a ; i++ )
           for( j = 0 ; j < a ; j++ )
                scanf("%d",&x[i][j]);
      for( i = 0 ; i < a ; i++ )
           for( j = 0 ; j <= i ; j++ )
                printf("%d ",x[i-j][j]);
      for( i = a ; i < 2 * a - 1 ; i++ )
           for( j = a - 1 ; j >= i - 3 ; j-- )
                printf("%d ",x[j][i-j]);
      getch();
}

Maybe, in order to get full credit point from this task, you should delete the "getch()" ?
I do not want to see your sorting algorithm...

#include <stdio.h>
#include<conio.h>

main()
{
      int x[100][100],a,i,j;
      scanf("%d",&a);
      for( i = 0 ; i < a ; i++ )
           for( j = 0 ; j < a ; j++ )
                scanf("%d",&x[i][j]);
      for( i = 0 ; i < a ; i++ )
           for( j = 0 ; j <= i ; j++ )
                printf("%d ",x[i-j][j]);
      for( i = a ; i < 2 * a - 1 ; i++ )
           for( j = a - 1 ; j >= i - (a-1) ; j-- )
                printf("%d ",x[j][i-j]);
}
Here's the correct code