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3. Evaluate 0&1is 0
Exercises - Priority of Operators
1. What are the answers to the following examples?
a. 22 + (12 * 1)
b. -6/-2>(45%7/2)-1
c. 10*2-(5+1)//5*2+15-1
2. In the example of the student and the college from the previous exercise on page “Exercises - Using
Logical Expressions” on page 27, if the parentheses were removed from the student's formula, what
would be the outcome for the college?
IF inexpensive | scholarship & reputable | nearby THEN
SAY "I'll consider it."
ELSE
SAY "Forget it!"
Remember the college is inexpensive, did not offer a scholarship, is reputable, but is 1000 miles away.
ANSWERS
1. The results are as follows:
a. 34 (22 + 12 = 34)
b. 1 (true) (3>3-1)
c. 32(20-2+15-1)
2. I'll consider it.
The & operator has priority, as follows, but the outcome is the same as the previous version with the
parentheses.
IF inexpensive | scholarship & reputable | nearby THEN
\_________/ \_________/ \_______/ \____/
true false true false
\ \___________/ /
\ false /
\_________________/ /
true /
\____________________/
true
Tracing Expressions with the TRACE Instruction
You can use the TRACE instruction to show how the language processor evaluates each operation of an
expression as it reads it, or to show the final result of an expression. These two types of tracing are useful
for debugging programs.
Tracing Operations
To trace operations within an expression, use the TRACE I (TRACE Intermediates) form of the TRACE
instruction. The language processor breaks down all expressions that follow the instruction and analyzes
them as:
>V> - Variable value - The data traced is the contents
of a variable.
>L> - Literal value - The data traced is a literal
(string, uninitialized variable, or constant).
>O> - Operation result - The data traced is the result
of an operation on two terms.
The following example uses the TRACE I instruction. (The line numbers are not part of the program. They
facilitate the discussion of the example that follows it.)
Using Variables and Expressions
Chapter 3. Using Variables and Expressions 29