In Steven Prata's book "C Primer Plus", there's a section on Type Conversions, wherein "The basic rules are" section has stated in rule 1:

Under K&R C, but not under current C, float is automatically converted to double.

http://www.9wy.net/onlinebook/CPrimerPlus5/ch05lev1sec5.html

Could someone explain what but not under current C means? Are there versions of C that auto-convert and versions that don't?

I'm trying understand if I have an expression that mixes floats and doubles, can I rely on C to promote floats to doubles when it's evaluated?

c floating-point type-promotion
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