In the C and C++ programming languages, #pragma once is a non-standard but widely supported preprocessor directive designed to cause the current source file to be included only once in a single compilation.
During sexual reproduction, fertilization of the ovum (n, 23 chromosomes) by the sperm (n, 23 chromosomes) restores the diploid number and creates a zygote (2n, 46) (awww..) that divides and grows by mitosis to form a multicellular human.
In a diploid state the haploid number is doubled. Thus, haploidy occurs during gamete formation. In particular, a human germ cell (a sperm or an egg cell) is haploid, which means it contains only one of each of the 23 chromosomes of the human genome, or it only has half the diploid (2n) number of a human somatic cell (which is 46). Gametes being haploid are essential particularly during fertilization.