Assignment and Data Conversion with Arithmetic Operators

Basic facts on assignment and conversion

1. Fact: Variables and values ALWAYS have a TYPE


• Primitive types: byte, short, int, long, float, double, char, boolean


2. Fact: Operators operate ONLY on values that have identical type


• Operators we are concerned with here: +, -, *, /, %, =


3. If the types do not match, the compiler will do some conversions automatically


4. If automatic conversions do not fix the mismatch, then the programmer must revise the expression and include explicit conversions.


5. The programmer can always add conversions

Explicit Conversions - Casting

1. Explicit conversions are called type casting
2. Put type in parentheses
3. eg int i = (int) 3.9; // Truncates to 3
4. Cast int into a float:
• eg float f = (float) 3; // converts 3 to 3.0

Two kinds of conversions: Widening and Narrowing

1. Narrowing
• From larger size value to smaller
• Can lose information
• eg int i = 3; byte b = (byte) i; // Does not lose info


• eg int i = 333; byte b = (int) i; // Will lose info


• eg int i; ... byte b = (int) i; // Might lose info


• eg float f; ... int i = (float) f; //Might lose info


• Compiler will NOT do automatic narrowing conversions
2. Widening
• From smaller size value to larger (usually)


• Does not lose information (might lose precision)


• eg byte b=3; int i=b


• eg int i=3; float f=i (can lose precision)

Automatic Conversions - Assignment Conversion

1. Compliler will automatically do widening conversion on RHS of assignment
• eg: float f = 3; // Automatic cast to float
• eg: byte b = 3; int i = b; // Automatic cast to int
2. Compliler will NOT automatically do narrowing conversion on RHS of assignment
• eg: int f = 3.0; // Syntax error
• eg: int i = 3; byte b = i; // Syntax error

Automatic Conversions - Promotion

1. Remember: all operators require the same type on both sides!


2. In expressions, compiler will use widening conversions to make both values the same type


3. consider byte b, int i, float f, double d;


4. 2 + d + 4 // Convert all values to double


5. 2 + d + f // convert all values to double


6. 2 + 3.0 // convert all values to double


7. 2 + f // convert all values to float


8. b + i + d // Convert all to double


9. b + i // Convert all to int


10. Type can change as evaluation progresses


11. eg: 2 + (3 + 4) * ( 5 + 6 ) % (2 * 4)

Order of operation

1. Parens
2. Mult
3. Add
4. Left to right when same level

Automatic Conversions - Assignment and Promotion

1. int i = 3 / 4;


2. int i = 10; int j = 25; int x = i / j; int x = j / i


3. int i = 10; int j = 25; int x = i % j; int x = j % i


4. float f = 3 / 4.0;


5. float f = 10.0; float g = 25.0; float x = f / g; float x = f / g


6. i + ( f * g ) / (i /