ブール式

true or false

• A Boolean expression 布尔表达式 evaluates to exactly one of two values: true or false.
• Conditions in if statements and loops are Boolean expressions.
• Store one in a boolean variable: boolean passed = score >= 60;
• Everything in selection and repetition rests on these true/false results.

Relational operators

• Relational operators 关系运算符 compare two values and give a Boolean:
• < less than, <= at most, > greater than, >= at least.
• == equal to, != not equal to.
• 5 > 3 is true; 4 == 5 is false.

The three families of operators: arithmetic, relational, and logical

== versus =

• == tests equality; = assigns — completely different jobs.
• x == 5 asks "is x equal to 5?" and gives true/false.
• x = 5 stores 5 in x.
• Using = where you meant == is a classic bug (and often a compile error in a condition).

Predicting the value

• To evaluate a Boolean expression, plug in the values and apply the operator.
• With x = 7: x < 10 → true; x == 7 → true; x != 7 → false.
• Read the operator carefully — <= includes equality, < does not.
• Being able to predict the result is the core skill for tracing code.