Learn to Program with C_ Learn to Program using the Popular C Programming Language ( PDFDrive )

Chapter 3 ■ Programs with Sequence Logic
Next, we need variables to store the interest and service charge. Since these may contain a
decimal point, we must use double variables—we call them interest and service.
Prompting for and reading the data are fairly straightforward, given what we have covered
so far. We need only emphasize that when numeric data is being entered, it must be a numeric
constant. We cannot, for instance, enter the average balance as $2500 or as 2,500. We must enter
it as 2500 or 2500.0 or 2500.00.
The calculation of the interest and service charge presents the biggest challenge. We must
specify the calculation in a form that the computer can understand and execute.
We cannot, for instance, write
interest = 6% of avgBalance;
or even
interest = 6% * avgBalance;
or
service = 50 cents per transaction;
We must express each right-hand side as a proper arithmetic expression, using appropriate
constants, variables, and operators. Therefore, “6% of average balance” must be expressed as
avgBalance*0.06
or
0.06*avgBalance
and “50 cents per transaction” must be expressed as
0.50*numTrans
or
numTrans*0.5
or something similar, even
numTrans/2.0
Printing the output is fairly straightforward. Even though, for example, we cannot use $ when
entering data for average balance, we can print a dollar sign in front of it when we print its value.
All we need to do is print $ as part of a string. How this is done is shown in the program. Similarly,
we print the interest and service charge labeled with a dollar sign.
We use the specification %3.2f for printing avgBalance. We intentionally use a small field
width of 3 so that avgBalance is printed using only the exact number of print columns needed
for printing its value. This ensures that its value is printed right next to the dollar sign. Similar
remarks apply to interest and service.
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