CSCI 15a: Chapter 6 (4 in second ed)

CSCI 15a: Chapter 6 (4 in second ed)

CSCI 15a: Notes Decisions
logic tests

Logical Expressions (produce Boolean results for Decisions)

Easy

Hopefully...

Let i₁=10, i₂=-20, i₃=30.

i₁ < 12          true
i₁ < 10          true
i₃ == i₁          false
i₁ != 2          true
i₁ < 10          false
i₂ > 0          false
2*i₁ == i₂+40          true
i₂*(-1) != i₁+i₁          false

Booleans can be stored as variables.

private boolean tooBig;
tooBig = true;
tooBig = i₁ > 10;

An expression like a < b < c is illegal.

Again let i₁=10, i₂=-20, i₃=30.

(i₁>10) || (i₁==10)         false || true          true
(i₁>10) || (i₁<0)          false || false          false
(i₁>0) && (i₁<5)          true && false          false
(i₁>0) && (i₁<20)          true && true          true

The && and || have lower precedence than the relational operators, but parentheses are still useful because they enhance readability.

The && and || are lazy operators that evaluate only the left operand only when that suffices.

(5 == 4) && ????
(5 != 4) || ????

Does it matter what the second operands are?

Harder

Now you write them.
Consider

Sum is less than 10
temp is strictly between -4.4 and 2.4
exactly one of the two numbers index and count is negative
2 floats, shot and target, are no more than 3 units apart
Z is negative, or both X and Y are non-negative
Two strings myString and yourString have the same length or the same value

Don't forget to try the problems in the book as well and see how well you know how to do these (Chapter 6 (4 in new edition)) has solutions at the bottom of the page. Also truth tables are good to remember.