Just about every language is written in C. Even GW-BASIC was written in C (most BASIC interpreters were written in assembly code at the time).
When all the code was being rewritten for Y2K, C was used because it was really the only language that was portable at the time, you could write the program on a PC, and then compile and configure it on a mainframe, or vice versa.
A more pertinent question would be what isn't wriiten in C.
Critical software, like interfaces, machine operation or database systems, are generally not written in C. That's because C code can be dense and obscure. If the original programmer retire or goes missing, and the system crashes, no one else may have a clue what they've actually coded. So a more explicable, higher level language is used and C is quarantined to use in system software where its power and access is useful.
Given that it is essentially a proxy war between the US and Russia, its quite possible the war could end without either side actually "winning".
Obviously the US will continue to support the war for as long as possible, and if that means turning ukraine to ash and destroying the economies of western europe, well that is a price they are willing to pay.
There are still shortages in Russia and if the gas and electricty shortages continue through winter that could be devastating in Russia. It wouldn't take that much to tip the country into chaos, what the response of the Russian govt to Ukraine would be - possibly using their really large missiles that can wipe out a whole village - is completely unknown.
We don''t really understand the mentality of the Ukraine govt. The fact that many western weapons seem to go missing before they reach the front and the coincidence of the Azerbaijan getting a pile of muntions just after deliveries to Ukraine may indicate that the aims of the Ukraine govt may not totally align with those of western europe.