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

Chapter 4 ■ Programs with Selection Logic
The astute reader may recognize that we do not even need the if statement.
Consider this:
mSum = m1 + m2; //add the meters
cmSum = cm1 + cm2; //add the centimeters
mSum = mSum + cmSum / 100;
cmSum = cmSum % 100;
where the last two statements come from the if statement.
We know therefore that this will work if cmSum is greater than or equal to 100 since, when that
is the case, these four statements are executed.
What if cmSum is less than 100? Originally, the last two statements would not have been
executed since the if condition would have been false. Now they are executed. Let us see what
happens. Using the example of 3m 25cm and 2m 15cm, we get mSum as 5 and cmSum as 40.
In the next statement 40 / 100 is 0 so mSum does not change and in the last statement
40 % 100 is 40 so cmSum does not change. So the answer will be printed correctly as
Sum is 5m 40cm
You should begin to realize by now that there is usually more than one way to express the logic of
a program. With experience and study, you will learn which ways are better and why.
4.4 The if...else Construct
Let us write a program for the following problem:
A student is given 3 tests, each marked out of 100. The student passes if his average mark is
greater than or equal to 50 and fails if his average mark is less than 50. Prompt for the 3 marks and
print Pass if the student passes and Fail if he fails.
We will write the program assuming it works as follows:
Enter 3 marks: 60 40 56
Average is 52.0 Pass
or
Enter 3 marks: 40 60 36
Average is 45.3 Fail
The following algorithm describes the steps required to solve the problem:
prompt for the 3 marks
calculate the average
if average is greater than or equal to 50 then
print "Pass"
else
print "Fail"
endif
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