3 - Function basics

Question 1

C++ comes with libraries of predefined functions that you can use in your programs. There are two kinds of functions in C++. Which?

Answer 1

1. Functions that return a value

2. Functions that don’t return a value (void functions)

Question 2

What is an “argument”?

Answer 2

The value a functions starts out with. E.g. :
sqrt (9.0);
Here, the double 9.0, is the argument.

Question 3

What is the difference between an argument and a parameter?

Answer 3

The formal parameter is what’s given in the function declaration, the actual argument is what’s passed when calling the function.

Question 4

What is this called?
#include

Answer 4

It’s an include directive, which names the library cmath. It indicates that the code below will be using functions from that library.

Question 5

There are include directives. Are there others?

Answer 5

There is also the using directive, which we use when we write:
using namespace std;

Question 6

The abs() and labs() functions give absolute values. Which library are they in?

Answer 6

They’re in the cstdlib (C Standard General Utilities Library) library.

Question 7

What do you use the cstdlib function abs for?

Answer 7

For producing the absolute value of a number type int.

Question 8

What do you use the cstdlib function labs for?

Answer 8

For producing the absolute value of a number type long.

Question 9

What do you use the cmath function fabs for?

Answer 9

For producing the absolute value of a number type double.

Question 10

What must you include and use in order to write 2^3 = 8 in C++?

Answer 10

You need to use the cmath library, and use the function pow(x,y).

Question 11

How do you round up numbers?

Answer 11

With the cmath function ceil(); Only works on doubles.

Question 12

How do you round down numbers?

Answer 12

With the cmath function floor(); Only works on doubles.

Question 13

How do you end the program from a place in your code?

Answer 13

With the cstdlib function exit(1); Only works on integers.

Question 14

How do you produce a “semi-random” number?

Answer 14

With the cstdlib function rand();

Question 15

How do you set the seed (starting value) for rand?

Answer 15

With the cstdlib function srand();

Question 16

Are there any restrictions on the use of the pow( ) function?

Answer 16

Many implementations of pow have a restriction on what arguments can be used. In these implementations, if the first argument to pow is negative, then the second argument must be a whole number. It might be easiest and safest to use pow only when the first argument is positive.

Question 17

What integer should you use as an argument to the exit ( ) function?

Answer 17

Any! But by convention, 1 is used for a call to exit that is caused by an error, and 0 is used in other cases.

Question 18

All standard functions have argument types they’re meant for. What happens if you use the wrong type?

Answer 18

In many cases, some automatic type conversion will be done for you by C++. However, the results may not be what you intended.

Question 19

What numbers will you have a chance of getting if you use the function rand ( ) ?

Answer 19

Any number in the range 0 to at least 32767. (32767 is the maximum two-byte positive integer).

Question 20

How do you scale the rand ( ) function, i.e. to give you random numbers between 0 and 10?

Answer 20

You have to use:

rand ( ) % 11.

Question 21

Why is the rand ( ) function not truly random?

Answer 21

A sequence of calls to the function rand will produce a sequence of numbers that appear to be random. However, if you could return the computer to the state it was in when the sequence of calls to rand began, you would get the same sequence of “random numbers”.

Question 22

Define: local variable.

Answer 22

Variables that are declared within the body of a function definition are called local variables.

Question 23

What is a function declaration? Give an example.

Answer 23

A function declaration is the part of the code that tells the compiler that a function exists. 
E.g: 
double TotalCost (int x, int y);

Question 24

What is a good way to make a function declaration comment?

Answer 24

One good way to write a function declaration comment is to break it down into two kinds of information called the precondition and postcondition.

Question 25

Is it necessary to return 0 from the main function?

Answer 25

The C++ standard says that you can omit the return 0 statement in the main part of the program, but many compilers still require it and almost all compilers allow you to include it. For the sake of portability, you should include a return + statement.

Question 26

What is meant by treating the function as a black box?

Answer 26

It’s a rule of programming. A programmer who uses a function is a program needs to know what the function does, but should not need to know how the function accomplishes the task.

Question 27

What are the two rules for writing a black-box function definition?

Answer 27

1. The function declaration comment should tell the programmer any and all conditions that are required of the arguments to the function and should describe the result of a function invocation.
2. All variables used in the function body should be declared in the function body.

Question 28

What is a global named constant, and should you use them?

Answer 28

A constant that is declared at the beginning of the program, outside the body of all the functions. Can be useful.

Question 29

What is a global variable?

Answer 29

A variable that is declared at the beginning of the program, outside the body of all the functions. They are seldom useful, and can make a program harder to understand and maintain.

Question 30

What is a block?

Answer 30

A block is some C++ code enclosed in braces { }. The variables in a block are local to the block, and so the variable names can be used outside the block for something else.