C is the "Natural Major Scale" since it doesn't require accidentals for the half steps to be in the right places.
If we want to build a major scale starting on a different pitch we must use accidentals to keep the half and whole steps in the right position.
The half steps still fall between B-C and E-F but these are the 3-4th and 6-7th scale degrees.
Major scales have half steps between 3-4 and 7-8,
This results in half steps between B-C and F-sharp to G and whole steps between the other steps- a major scale.
Using accidentals, a major scale can be built on any note and keeping half steps between 3-4 and 7-8 and whole steps between the other scale degrees.