Answer:

Since the answer is mysteriously zero, you should suspect that one of the variable names has been changed. The name COSTS in the PRINT statement is not the same as COST in the third statement.

' Cost of renting a car
' $26.59 per day
' 31 cents per mile, plus
' 3 days and 253 miles
'
LET DAYS = 3
LET MILES = 253
LET COST = 26.59 * DAYS + 0.31 * MILES
PRINT "Cost is", COSTS
END                  ^
                   wrong

Changing the Contents of a Variable

Remember that a variable is a small amount of computer memory that has been given name. The contents of computer memory can be changed. In your program you can do this by using a LET statement with a variable that already has something in it. Look at the following program:

' Changing the contents of a variable
'
LET NUMBER =  23.5     ' create NUMBER, put 23.5 into it
PRINT "First", NUMBER  ' look in NUMBER to find a value to print
LET NUMBER = 45.1      ' put 45.1 into NUMBER (erasing the 23.5)
PRINT "Second", NUMBER ' look in NUMBER to find a value to print
END

Execution starts with the first statement, the first LET statement. This is the first time NUMBER is used, so memory is found for it. Then 23.5 is put into it. into it:

`NUMBER`
23.5

Now the first PRINT statement executes. It looks into NUMBER, finds 23.5, and prints that to the screen. The value in NUMBER has not changed.

Answer:

Changing the Contents of a Variable

QUESTION 19: