chapter7 ........\fork an vfor k.c ........\p7.1.c ........\p7.10.c ........\p7.11.c ........\p7.12.c ........\p7.13.c ........\p7.14.c ........\p7.15.c ........\p7.16.c ........\p7.17.c ........\p7.18.c ........\p7.2.c ........\p7.3.c ........\p7.4.c ........\p7.5.c ........\p7.6.c ........\p7.8.c ........\p7.9.c