1. Engr 0012 (04-1) LecNotes 25-01

2. Arrays - review Declaring an array
use defined constant to specify maximum number of elements in the array
// preprocessor commands
#define MAXARRAYSIZE 100 …
main() { 
// variable declaration
double length[MAXARRAYSIZE], // array of lengths
width[MAXARRAYSIZE]; // array of widths
int actualsize, // actual amt in use
i; // loop index
type of
values
meaningful
name
maximum number of
elements in [ ]
arrays do not need to be “full” -
need to keep track of how much is
actually used
Engr 0012 (04-1) LecNotes 25-02

3. Arrays Memory management
compiler remembers only location (address of) first location
&length[0]  length
&length[0]
&length[MAXARRAYSIZE-1] …
declaration sets aside MAXARRAYSIZE memory locations
capable of holding specified type of information
&length[actualsize-1]
do not need to use entire allocation of memory
==> need to keep track of actualsize
Engr 0012 (04-1) LecNotes 25-03

4. Arrays Using arrays … &length[0] &length[MAXARRAYSIZE-1]
&length[actualsize-1]
length[0]
length[18]
length[8]
length[-2]
length[260]
accessing values - name and index
Engr 0012 (04-1) LecNotes 25-04

5. Two dimensional arrays - tables/matrices
N rows
M columns
Dimension: NxM (rows x columns)
if N = M (i.e., dimension NxN)
square matrix
still require all values be of same type
Engr 0012 (04-1) LecNotes 25-05

6. Two dimensional arrays - declaring
use defined constants to declare
dimensions
// preprocessor commands
#define MAXROW 10
#define MAXCOL 10 …
main() { 
// variable declaration
double length[MAXROW][MAXCOL]; // table of lengths
int actrows, // actual rows in use
actcol, // actual col in use
i,j,k; // loop indices
#define MAX2D 10
if square matrix, only need one size
specify rows and columns
double length[MAX2D][MAX2D]; // table of lengths
keep track of amount
in use
Engr 0012 (04-1) LecNotes 25-06

7. Two dimensional arrays - using
length[1][2]
value in 2nd row, 3rd column
&length[6][4]
address of value in 7th row, 5th column
&length[0][0]  length
address of first element
Engr 0012 (04-1) LecNotes 25-07

8. [ ] tells that the variable is an array
Arrays - function prototypes/parameter lists
// preprocessor commands
#define MAXARRAYSIZE 100 …
main() { 
// variable declaration
double length[MAXARRAYSIZE], // array of lengths
width[MAXARRAYSIZE]; // array of widths
int actualsize, // actual amt in use
i; // loop index
[ ] tells that the variable is an array
// function prototypes
int getarray( double length[ ] );
double avearray( double length[ ], int actsize );  
used to return number of
values actually in use
need to send amount
actually in use
Engr 0012 (04-1) LecNotes 25-08

9. Arrays - calling statements/parameter lists
// preprocessor commands
#define MAXARRAYSIZE 100
// function prototypes
int getarray( double length[ ] );
double avearray( double length[ ], int actsize );   …
main() { 
// variable declaration
double length[MAXARRAYSIZE], // array of lengths
width[MAXARRAYSIZE]; // array of widths
int actualsize, // actual amt in use
i; // loop index
name w/o [ ]
// calling statement
actualsize = getarray( length );
ave = avearray( length, actualsize ) 
==> sending address
of first element
Engr 0012 (04-1) LecNotes 25-09

10. 2D arrays - function prototypes/parameter lists
// preprocessor commands
#define MAX1D 100
#define MAX2D 100 …
main() { 
// variable declaration
double oned[MAX1D]; // 1D array
double twod[MAX2D][MAX2D]; // 2D array
int onedact, // 1D array in use
actrows, // actual amt in use
i,j,k; // loop indices 
need to send amount
in use
// function prototypes
void fill( double onedarray[], int used1D,
double twodarray[][MAX2D], int used2D );  
need to specify maximum number
of columns
Engr 0012 (04-1) LecNotes 25-10

11. 2D arrays - calling statements/parameter lists
// preprocessor commands
#define MAX1D 100
#define MAX2D 100 …
main() { 
// variable declaration
double oned[MAX1D]; // 1D array
double twod[MAX2D][MAX2D]; // 2D array
int onedact, // 1D array in use
actrows, // actual amt in use
i,j,k; // loop indices 
// function prototypes
void fill( double onedarray[], int used1D,
double twodarray[][MAX2D], int used2D );  
// calling statement
fill( oned, onedact, twod, actrows );
local array name w/o [] ==> sending address
Engr 0012 (04-1) LecNotes 25-11