Control Flow - Conditional Statement

LT4 Control Flow - Conditional Statements

Syntax Summary

1. Keywords
   • if, else
   • switch, case, default
   • break, continue
2. Punctuators
   • (), {},
   • :
   • ? :
3. Operators
   • ==, !, !=, >, >=, <, <=, &&, ||

Logical expression

0 is false, false is 0

• Any value other than 0 / false deems to be true in logic expression. (&&0=0)
• However, true = 1 in C++

! - Logical NOT

Inverses the boolean value of the operand

Predecence of Logical Operators

1. * / %
2. + -
3. < <= > >=
4. == !=
5. && ( Predecence of Logical AND && is prior than logical OR || )
   • 1 && 0 || 1 && 1 == 0 || 1 == true
6. ||
7. ? : (RTL)

Compound Statement: Grouped in { }

if ... else if ... else ...

if( ){

}else if( ){

}else{

}

Here are the TRAPS

Be aware of Empty Statements if(1==2); cout<<"1 = 2";

Where I Fell in the Mid-Term

Nester: an if-else statement is included in an if or else statement (Nearest Predecence)

Be aware of = and ==

= operators always return true, unless RHS == 0 ie false

Short-Circuit Evaluation

Only execute the Former Operand when the outcome is known

• For &&: when former-statement == false (already known to be false)
• For || when former-statement == true (already known to be true)

Official explanation: Improve program efficiency

switch statement

• The switch expression must be an Integer (int, long, short, char)
• The case const-expression must be constsnts

switch (expression){
    case const-expr1: // the case expression must be Constant
        statement-1;
        break;
    case const-exprn:
        statement-n;
        break;
    default:
        statement-default;
}

Conditional Operator: expr1 ? expr2 : expr3

• Sequence of Evaluation:

1. expr1 is evaluated
   1. if true, expr 2 is evaluated and returned
   2. if false, expr 3 is evaluated and returned