Topic 9 - Functions

Question 1

What do functions consist of:

Answer 1

1) Declarations

2) Statements

Question 2

Do you need a return statement in C89? If not, what happens when no return statement?
In C99? If not, what happens when no return statement?

Answer 2

C89 = don't need it; default returns value of type int
C99 = omitting return type is illegal

Question 3

In C89, where must you place variable declarations ?

In C99?

Answer 3

C89 = Must come first before all statements in the body of a function.
C99 = variable declarations and statements can be mixed, as long as each variable is declared prior to the first statement that uses the variable

Question 4

Can variables declared in the body of a function be examined or modified by other functions?

Answer 4

No.

Question 5

How do you make it clear that you are deliberately discarding the return value of a function?

Answer 5

Put (void) in front of the function call.

Question 6

Does C89 care where definition of a function is placed relative to where it is being called?
How about C99?

Answer 6

No - C89 does not require that the definition of a function precedes its calls
C99 will give you an error if calling a function without first providing a definition or declaration of the function.

Question 7

Does it matter where we place the function’s definition?

Answer 7

Yes.

Question 8

What happens if a function’s definition is placed after where it is being called?

Answer 8

• compiler encounters function call but has no information on it
• doesn’t produce an error message but assumes the function returns an int and hopes for the best
• this is called an IMPLICIT DECLARATION

Question 9

What is an implicit declaration?

Answer 9

When function’s defn is after its call and the compiler assumes its returning an int type

Question 10

What is default argument promotions?

Answer 10

The compiler is unable to check that we are passing to the function the right number of arguments and that the arguments have the proper type:

• float arguments to be converted to double
• char and short arguments convert to int

Question 11

Give 2 ways to remedy the problem of call-before-definition:

Answer 11

1) function den precedes call

2) use function declarations

Question 12

What is a function declaration’s syntax?

Answer 12

return-type function-name (parameters);
ex:
double average(double a, double b);   /* DECLARATION */

Question 13

Can you omit the parameter names? (As long as you still specify the parameter types)?

Answer 13

Yes, this is called function prototyping

Question 14

Does any changes made to the parameter during the execution of the function affect the arguments?

Answer 14

No.

Question 15

Does argument decomposition work?

Answer 15

No.

Question 16

In terms of Argument Conversions: if the compiler has encountered a prototype prior to the call - what happens?

Answer 16

The value of each argument is implicitly converted to the type of the corresponding parameter as if by assignment

Question 17

In terms of Argument Conversions: if the compiler has NOT encountered a prototype prior to the call - what happens?

Answer 17

• compiler performs default argument promotions
• float arguments to be converted to double
• char and short arguments convert to int

Question 18

Is there an easy way for a function to know the length of an array that has been passed as an argument?

Answer 18

No, usually have to pass a second argument being the length of the array.

Question 19

Do you put the brackets in an array argument in the arguments section of the function header?

Answer 19

No:
total = sum_array(b[], LEN);
is wrong. This is right:
total = sum_array(b, LEN);

Question 20

Can a function change the elements in an array parameter where the chance is reflected in the corresponding argument?

Answer 20

Yes.

Question 21

If a parameter is a multidimensional array, which dimension can the length be left unspecified?

Answer 21

the length of the first dimension.

Question 22

How do you remedy the annoyance of not being able to pass multidimensional arrays with an arbitrary number of columns?

Answer 22

Use arrays of pointers (chapter 13)

Question 23

Do you need a return statement in a void function?

Answer 23

No but you can have it if you wish but unnecessary.

Question 24

Give 2 ways to terminate a program:

Answer 24

1) return statement in main

2) exit function anywhere in the program if you’ve included

Question 25

How do you improve quick sort program’s performance?

Answer 25

• Improve the partitioning algorithm
• use a different method to sort small arrays
• make quick sort non recursive