[Solved] What does a ! operator mean if put in front of a variable?

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!ok is the same as ok == 0.

Remember that in C, any non-zero scalar value in a Boolean context means “true” while zero means “false”. It’s a common C idiom to write !foo instead of foo == 0. It works for pointers as well:

FILE *foo = fopen( "some_file", "r" );
if ( !foo )
{
  fprintf( stderr, "could not open some_file\n" );
  return EXIT_FAILURE; 
}

So, while ( x ) is the same as while ( x != 0 ), and while ( !x ) is the same as while ( x == 0 ).

solved What does a ! operator mean if put in front of a variable?