▁statement ▁by ▁statement , ▁which ▁tells ▁us ▁something ▁about ▁the ▁execution ▁model ▁of ▁the ▁language . ▁It ▁tells ▁us ▁that ▁statements ▁are ▁ind iv is ible ▁units ▁of ▁work ▁and ▁that ▁they ▁proceed ▁in ▁the ▁same ▁order ▁as ▁their ▁s ynt actic ▁appearance ▁in ▁the ▁code ▁( except ▁when ▁a ▁control ▁statement ▁such ▁as ▁IF ▁or ▁WH I LE ▁mod ifies ▁the ▁order ). ▁By ▁stating ▁the ▁order ▁in ▁which ▁statements ▁are ▁executed , ▁the ▁language ▁spec ▁has ▁stated ▁constraints ▁on ▁the ▁order ▁of ▁performing ▁units ▁of ▁work . ▁The ▁C ▁language ▁actually ▁has ▁an ▁additional ▁level ▁to ▁its ▁execution ▁model , ▁which ▁is ▁the ▁order ▁of ▁preced ence . ▁It ▁states ▁the ▁rules ▁for ▁the ▁order ▁of ▁operations ▁within ▁a ▁single ▁statement . ▁The ▁order ▁of ▁preced ence ▁can ▁be ▁viewed ▁as ▁stating ▁the ▁constraints ▁on ▁performing ▁the ▁units ▁of ▁work ▁that ▁are ▁within ▁a ▁single ▁statement . ▁So , ▁"; " ▁and ▁" IF " ▁and ▁" W HI LE " ▁cover ▁constraints ▁on ▁the ▁order ▁of ▁statements , ▁while ▁order ▁of ▁preced ence ▁covers ▁constraints ▁on ▁work ▁within ▁a ▁statement . ▁Hence , ▁these ▁parts ▁of ▁the ▁C ▁language ▁specification ▁are ▁stating ▁the ▁execution ▁model ▁of ▁the ▁C ▁language . ▁ ▁Exec ution ▁models ▁can ▁also ▁exist ▁independently ▁from ▁programming ▁languages , ▁examples ▁of ▁which ▁would ▁be ▁the ▁P OS IX ▁Thread s ▁library , ▁and ▁H adoop ' s ▁Map - R edu ce ▁programming ▁model . ▁The ▁implementation ▁of ▁an ▁execution ▁model ▁can ▁be ▁via ▁compiler , ▁or