11 + 12 + 13. Arrays

Question 1

array

Answer 1

collection of data items of the sametype

eg. array of 5 names

Question 2

arrays are ordered

Answer 2

• there is an order to slots in an array
• each slot is numbered
• in C++ slots numbered from 0 upwards

Question 3

need for arrays

Answer 3

• allows to store lots of values at one time

- can print in order of slots

Question 4

declaring arrays syntax

Answer 4

data_type array_name[size];

must put declared size in the square brackets

Question 5

explain this array:

double grades[6];

Answer 5

declares an array

• called grades
• that can hold up to 6 values
• of type value

the slots in this array are are numbered 0 to 5

Question 6

declaring arrays - size of array

Answer 6

size of array must be known

can’t do this:
int size;
cin&raquo_space; size;
int array[siz];

Question 7

accessing array elements

Answer 7

in array[x], x is the subscript/index

Question 8

how to access array elements examples

Answer 8

cin&raquo_space; grades[1]
-reads in a value for slot 1

x = grades[i]
-gets value of the slot numbered by whatever value i currently has and ssigns it to x

Question 9

array index expressions

Answer 9

index can be any expression whose value is an integer between 0 and (arraysize - 1)

eg. grades[i+2]

Question 10

For loops and arrays

Answer 10

use for loops for handling all elements of an array

Question 11

for loops and arrays syntax

Answer 11

for (i = 0; i

Question 12

note on for loop condition

Answer 12

use arraysize in the FOR conditions rather than writing the number

Question 13

index out of range errors

Answer 13

-occur in trying to access an array element beyond the end of the array

Question 14

what will happen?

double grades[6];
grades [7] = 78;

Answer 14

will overwrite memory locations storing some other variable

Question 15

what will happen?

double grades[6];
for (i = 1; i <=6; i++)
…

Answer 15

possibly disastrous

Question 16

restrictions on array processing

Answer 16

• cant assign a whole array to another, have to copy element by element (slot by slot) - use for loops to do this
• cant cin a whole array of elements - must read in slot by slot using for loop

Question 17

syntax of passing array elements to another array

Answer 17

for (i = 0; i < arraysize; i++) {
array[i] = array2[z];
}

Question 18

syntax of passing in values into each slot of an array

Answer 18

for (i = 0; i < arraysize; i++) {
cin&raquo_space; array[i];
}

Question 19

specific example - array of month names

Answer 19

• a program to map month numbers to month names
• create array of month names
• use slots numbered 1 to 12, leave 0 blank to make it easier to read

Question 20

array slots

Answer 20

not every slot has to be filled

Question 21

passing in array elements to functions

Answer 21

for non-void functions, arrays should match function data type

Question 22

functions that take arrays

Answer 22

you can pass a whole array into a function or just an element from an array

function should be told size of array if you are passing a whole array

Question 23

passing arrays into functions syntax + declaration of the function

Answer 23

declaration of the function:
datatype function(datatype array[], int size)

calling the function:
function(arrayname, ARRAY_SIZE);

Question 24

functions and array elements

Answer 24

functions modify elements of array, array parameters are like reference parameters, even though they don’t have an ampersand

Question 25

reading into arrays

Answer 25

functions can be used to read in values into an array as array parameters are modifiable

Question 26

read_array function syntax

Answer 26

void read_array(datatype a[], int arraysize) {
  int i;
  for (i = 0; i < arraysize, i++)
     cin >> a[i];
}

note –> can initialise i in for loop

Question 27

const modifier

Answer 27

used if you dont want function to change elements in array

Question 28

syntax of const modifier

Answer 28

datatype function(const datatype a[], int size);

Question 29

remember when passing arrays into functions

Answer 29

• functions processing arrays should take a size parameter

- if you don’t want to modify array, use const modifier

Question 30

not recommended

Answer 30

generally a function shouldn’t both update array elements and return a value

Question 31

how to use arrays where we don’t know how many slots will be filled

Answer 31

1) declare array big enough to handle max possible problem siz: DECLARED_SIZE
2) keep track of how many slots are filled: array_size or eg. num_Grades
3) use the latter number in FOR loops that process the array

Question 32

read to sentinel function syntax

Answer 32

check notes

Question 33

calling readtosentinel function syntax

Answer 33

readtosentinel(array, MAX_SIZE, count, sentinel);

note -> write what the sentinel is, or initialise the sentinel at the start or before the main and write sentinel

Question 34

declaring array size - good practice

Answer 34

this is good practice:
const SIZE = 6;
double array [SIZE];

for … blah blah

instead of writing double array[6];

Question 35

why declare array size like this

Answer 35

-will make SIZE easier to change later if we want to

Question 36

finding max/min of set of numbers

Answer 36

-safer to set maxes and mins to the first value obtained instead of setting it to zero initially

syntax of finding max or min values in notes

Question 37

index out of range errors

Answer 37

-watch out for when doing things such as:

double grades[5];
grades[i] = grades[i + 1];

what would happen when i = 4? There is no slot 5!

Question 38

read and print function

Answer 38

• always void, do not return anything

- print arrays should use const so as not to change the array