Intermediate C Programming

112 Intermediate C Programming

that have problems, then valgrind will not detect any problems. This is not a limitation in

valgrind, but more an indication of what type of tool it is. This is a limitation in how you

write test cases. You need to think how your program may fail and then test the potential

problems. Good tests can make valgrind invaluable. Note that this is another reason why

passing test cases does not guarantee that the program is correct. If the test cases do not

test the problematic parts, then the problems are undetected.

How could it be possible that some parts of the program are not executed? This is

because most programs have many if conditions. It is extremely diﬃcult—practically

impossible—to design test cases that can check every combination of these conditions. For

each if condition, the condition can be true or false. Hence, there are two possibilities. If

there are n if conditions and they are independent, there are 2

possibilities. As a point of

reference, in one weekly homework for my class at Purdue University, the sample solution

has 25 if conditions, about 2

= 34 million possibilities. Can you create 34 million test

cases? Obviously a brute-force approach is impossible, but the task is signiﬁcantly eased by

examining the logic of the program. Even though there are 25 if conditions in the sample

solution mentioned, there are not 34 million paths through the code because some condi-

tions are related. Careful reasoning is required to make this type of analysis. It is certainly

possible that some problems are not detected when this homework assignment is graded.

Table of Contents for Intermediate C Programming