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Pętla do-while najpierw się RAZ wykona a później dopiero jest
sprawdzany warunek i pętla ewentualnie dalej się będzie wykonywać.
Pętla do sprawdza warunek na początku, w naszym przykładzie nie wykona się
console.log('===== pętla DO WHILE =====');
} while (liczba<=0);
console.log('===== pętla DO =====');