Operator Precedence

1
Operator Precedence

• What is the order of evaluation in the following
  expressions?

a b c d e
a b c - d / e
1
2
3
4
3
1
4
2
a / (b c) - d e
2
1
4
3
a / (b (c (d - e)))
4
3
2
1
88
2
Example

• Givens X, Y, Z (three numbers)
• Result M (the largest given value)
• Header M?Max3( X, Y, Z )
• Two solutions
• sequence of branch structures
• nested branch structures
• Translate the latter into Java

m x if ( y gt m ) m y else //
do nothing if ( z gt m ) m z else
// do nothing
M ? Y
Ø
Z gt M ?
M ? Z
Ø
106
3
Translation
if ( x gt y ) if ( x gt z ) m x
else m z else if
( y gt z ) m y else
m z
108
4
Translation
a 0 b 0 if ( x gt 0 ) a 5 b a
1 else if ( y gt x ) a 4
b 0 else // do nothing

111
5
Translate to Program

• import java.io.
• class Sum1ToN
• public static void main (String args )
  throws IOException
• // read the input
• System.out.println("Enter a positive
  integer N.")
• int n CSI1100.readInt( )
• // initialize counter and accumulator sum
• int count 1
• int sum 0
• // loop
• while (count lt n)
• sum sum count
• count count 1
• // output the result

114
6
FOR loop to add 1 to N
Sum ? 0
Count ? 1
Count ? N ?
true
Sum ? Sum Count
false
Count ? Count 1

• Translate

sum 0 for ( count 1 count lt n count
count 1 ) sum sum count
117