2.3 if Statements

1. Exam Points

• if (only if)
• if...else
• if...else-if...else
• Note:
  • First check what a question asks (x or y, correct(√) or not correct(X)).
  • if an if or else block contains multiple statements, enclose them with {}
  • multiple if statements will be executed one after another.
  • in the if-else if statement, only one block will be executed (first match).

2. Knowledge Points

(1) if Statements

• Selection statements change the sequential execution of statements.
• An if statement is a type of selection statement.
• Different code segments will be executed based on the value of a Boolean expression.
• Types of if statements:
  • One way selection (if)
    
    
    • Multiple if statements will be executed one after another.
      
  • two-way selection (if-else)
    
  • multiway selection (if...else if...ese)
    
    
    • Only one block will be executed.
    • Rule: execute the first matched block.
    • Multiple else-if(optional) blocks are allowed
    • You may add an else(optional) block in the end or not.
• A special case
  • In a multiway selection, if the first few conditions cover all the cases, then the remaining conditions are of no use.
  • Example:
    
    
    • In this example, score >= 90 and score < 90 cover all the cases, so the remaining two conditions will never be executed.

3. Exercises

• Practice
• Solution