2、if语句的3种形式:1)if(表达式)语句如if(x>y)printf(“%d”,x);2)if(表达式)语句1else语句2如if(x>y)printf(“%d”,x);elseprintf(“%d”,y);3)if(表达式1)语句1elseif(表达式2)语句2elseif(表达式3)语句3...elseif(表达式m)语句melse语句n