Hoare logic for the set of while-programs with the first-order logical language L and
the first-order theory T ⊂ L is denoted by HL(T ). Bergstra and Tucker have pointed out
that the complete number theory Th(N) is the only extension T of Peano arithmetic PA
for which HL(T ) is logically complete. The completeness result is not satisfying, since it
allows inputs to range over nonstandard models. The aim of this paper is to investigate
under what circumstances HL(T ) is logically complete when inputs range over the standard
model N. PA+ is defined by adding to PA all the unprovable 1-sentences that describe the
nonterminating computations. It is shown that each computable function in N is uniformly
1-definable in all models of PA+, and that PA+ is arithmetical. Finally, it is established,
based on the reduction from HL(T ) to T , that PA+ is the minimal extension T of PA for
which HL(T ) is logically complete when inputs range over N. This completeness result has
an advantage over Bergstra’s and Tucker’s one, in that PA+ is arithmetical while Th(N) is
not.