Module 10: Variables & Pointers

Question 1

type modifiers

Answer 1

change the width of data types

Question 2

name of an array

Answer 2

acts as the starting address where the array is stored in memory; the equivalent of an assembly label

Question 3

casting

Answer 3

allows programmer to forcibly convert one data type to another

Question 4

typedef

Answer 4

allows you to give known type a new name

Question 5

pointer

Answer 5

variable that can only contain the memory address of another variable

Question 6

dereference

Answer 6

the act of looking up the value that the pointer points to

Question 7

• operator

Answer 7

the “address operator” in C. if it precedes any variable, it will determine its runtime address

Question 8

void

Answer 8

officially a data type but really more of a keyword to indicate the absence of data

Question 9

void* pointer

Answer 9

a typeless pointer, so it can point to any type of data. one limitation is that it cannot be dereferenced; you would have to cast it to a typed pointer in order to dereference it. the void* pointer’s purpose is to allow for the passage of a memory address but not to allow dereferencing

Question 10

implicit cast

Answer 10

smaller to bigger conversions are implicit; compiler does this for you

Question 11

explicit cast

Answer 11

bigger to smaller conversions you must do explicitly
int a = 5 ;
float b = 5.0 ;
a = (int) b ;

note that the b is truncated, fraction is lost, no rounding

Question 12

why do we need pointers in C?

Answer 12

1. helps us to pass addresses to functions instead of data
2. recall that in C we pass copies of local variables to functions in order to ensure their local scope is protected
3. pointers allow us to break scope and send address of a local variable

Question 13

pointers vs. arrays

Answer 13

name of array: a label for an address in data memory that contains data

pointer: a variable that contains a memory address of a variable that contains data

you cannot change the address of an array (it is a label!)

you can change the address held onto by a pointer

you can use the [ ] operator as a dereferencing operator on a pointer

• helpful if pointer points to an array
• don’t let that confuse you into thinking that a pointer is an array!

you can do pointer arithmetic on a pointer but NOT on an array!

passing the name of an array is the same as passing a memory address

Question 14

intitializing pointers

Answer 14

ALWAYS initialize! this will help to avoid unexpected behavior in your program.

Question 15

constant in C

Answer 15

#define - you can change the next time you compile
#define statements are like assembly directives (no space allocation)

const types - constants that never change
space allocation!

Question 16

CONST applied to pointers

Answer 16

pointer to a constant:
we CAN change what the pointer points to but not the value of what it points to

constant pointer to a variable:
we can’t change what pointer points to but we can change the value of what it points to

constant pointer to a constant variable:
we can’t change what pointer points to
we can’t change the value of what it points to

Question 17

3 basic regions of data memory in C

Answer 17

1. stack (local variables, arguments, returns)
2. global/static region (global vars, static vars)
3. heap (dynamic space)

Question 18

2 basic storage classes

Answer 18

automatic variables: lose their values when their block terminates (since they are on the stack)
-arguments, return types, local variables

static variables: retain values between invocations
-global variables are a type of static variable