Given the two C$++$ code snippets below, in which situation their output will certainly not be the same?

$...$

a$++$;

while $($a $<5)\{$

std::cout $<<$ a $+$ b;

a$++$;

$\}$

$...$

do $\{$

a$++$;

std::cout $<<$ a $+$ b;

$\}$ while $($a $<4)$;

if a is greater than $3.$

if a is smaller than $4.$

if a is smaller than b$.$

if a is greater than b$.$