summary：

　　1: if, elsif, else.注意结束if时后面加end

　　2: unless, else

 

• How to use if, else, and elsif
• How to use comparators / relational operators like ==(相等), !=（不等）, <, <=, >, and >=

How to use boolean / logical operators like &&（与）, ||（或）, and !（非）

1 a = 102 b = 113 if a < b4   print "a is less than b!"5 elsif b > a6   print "b is less than a!"7 else8   print "b is equal to a!"9 end

 

1 problem = false2 print "Good to go!" unless problem3 #除非有问题（problem=true时不打出来），否则打印出来

 

多个逻辑运算结合，用括号 括起来

1 ( 1 == 1 ) && ( 2 == 2 )  // true2 ( 1 == 2 ) || ( 2 == 2 ) // true3 !( false ) // true