单元格A1<45时B1为N45<=A1<100时B1为C45100<=A1<500,B1为C100500<=A1<1000,B1为C500A1>=1000时,B1为C1000
=IF(A1<45,"N",LOOKUP(A1,{0,"N";45,"Q+45";100,"C+100";500,"C+500";1000,"C+1000"}))