Lecture 26 – November 27, 2007

Returned graded work and quizzes

Discussed answers to quizzes

For final:

• know 2s complement representation of positive and negative numbers
• know how to convert base 10 numbers into base 2 and vice versa
• know how to determine the address of an element in a two-dimensional array (be careful to pay attention as to whether the array is stored in row-major or column major order).
• Know the definition of a (abstract) data type and be able to indicate appropriate operations for a given data type.
• Know why we use two’s complement representation on a computer instead of sign-magnitude,

Showed traces of some Prolog programs

/*----------------------------------------------------------------------

* "Agatha Christie" Problem

* Who was the killer?

*

* Alice, her husband, son, daughter,

* and brother are involved in a murder.

* One of the five killed one of the other

* four.

*

* 1. A man and a woman were together in the bar at the time of the murder.

* 2. The victim and the killer were together on the beach at the time of the murder.

* 3. One of the children was alone at the time of the murder.

* 4. Alice and her husband were not together at the time of the murder.

* 5. The victim's twin was innocent.

* 6. The killer was younger than the victim.

* NOTE: you may assume that the father is older than the son and daughter

*----------------------------------------------------------

Alternate problem;

If my client is guilty, then the knife was in the drawer. Either the knife was not in the drawer or Jason Pritchard saw the knife. If the knife was not there on October 10, it follows that Jason Pritchard did not see the knife. Furthermore, if the knife was there on October 10, then the knife was in the drawer and also the hammer was in the barn. But we all know that the hammer was not in the barn. QUESTION: is the client guilty?
Chapter 7-

• Arithmetic expressions
• Precedence rules – order of operations
• What type of operands go with what type of operators
• 2*3*4 - evaluated left to right
• 2**3**4 – evaluated right to left
• Overloaded operators
• +
• Integers - addition
• Floats - addition
• Strings – concatenation
• Performing an operation on two objects – possible in Ada and in C++ but not in Java or C
• Type conversions
• Widening vs narrowing
• Implicit vs explicit
• Implicit happens without your having to explicitly tell it to do the conversion as in Snobol where we can make a variable which is an integer become a string like magic
• Explicit conversion is really “like” a function call
• Relational and Boolean expressions
• Relational operators: 6 of them: GT, LT, GE, LE, EQ, NE
• Boolean operators : and, not, or, xor
• Relational expressions evaluate to true or false
• Boolean expressions evaluate to true or false
• Short Circuit Evaluation
• Only evaluates the operands necessary to determine T or F
• AND – if first operand is false, 2^nd isn’t evaluated
• OR – if first operands is true, 2^nd isn’t evaluate
• Java’s ANDs and ORs statements default to short circuit
• Ada has special operators for short circuit
• Normal is AND and OR
• Short circuit is AND THEN and OR ELSE
• In C
• Normal AND is &, normal OR is |
• Short circuit AND is && and short circuit OR is ||
• Assignment Statements
• Different symbols for the operator in different languages
• = in FORTRAN
• := in Pascal
• When assignment can be carried out?
• Mixed-mode
• Ada example showing that mixed mode arithmetic isn’t allowed (explicit conversion necessary.

o procedure testMixedMode is
i,j : integer;
x,y : float;

begin
x :=3.14159;
i := 17;
-- y := x + i;
y := x + float(i);
end testMixedMode;

We will go over parameter passing modes on Thursday