[C++] Chap 05 - Arrays

Arrays

• A collection of data of a same type
• Declare the array : allocates memory int score[5];
• Array size must be a constant
• Index “out of range” : No warning, but possibly disastrous results

int score[5];
score[1]=1; 
/*
score[1] : Indexed or subscriped var, element
1 : index or subscript, numbered from 0 to size-1
*/

Use of brackets

• In declaration, specifies the SIZE of array
• anywhere else, specifies a subscript

Array in memory

• Array declarations allocate memory for entire array
• Sequentially-allocated (addresses allocated “Back to back”)

Array size / Initializing arrays

• Recommended to use defined/named constant for array size
• Initializing with brackets int child[3] = {2, 12, 1};
• If fewer values than array size are supplied : fills the rest with zero of array base type
• If array-size is left out, declares array with size required based on number of initialization values

	int b[] = {5, 12, 11}; // size = 3
	int b[4] = {5, 12, 11}; // size=3, b[3]=0;

Arrays in functions

• Each indexed variables can be a function parameter
• Entire arrays can be passed as “one entity”

Entire arrays as Arguments

• Argument passed in function call is array name
• Typically send size of array as int formal parameter

void fillUp(int a[], int size);
//formal array parameter : not a call-by-reference parameter
//but similar in some sense
// declaring with int a[4] is same as int a[] 
// actually int* a
int main() {
		int a[3] = {1, 2, 3}
		fillup(a, 3); //No bracket!

• When array argument is used,
  • only the first part is passed(with base type matched)
  • the size of array is not passed)

Const parameter modifier

• To protect array contents from modification, use const

void stw(int a[], int sizeOfa) {
    for (int i = 0;i<sizeOfa;i++) {
        cout<<a[i]<<" ";
    }
    cout<<endl;
}
void stw2(const int a[], int sizeOfa) {
    for (int i = 0;i<sizeOfa;a[i]++) {
    //because a is const, a[i]++ generates error
    //if const not used, it will result in an infinite loop
        cout<<a[i]<<" ";
    }
    cout<<endl;
}

Functions that return an array

• Cannot return array.
• Required to use ‘pointer’

Multidimensional Arrays

• Arrays with more than one index

char page[30][100];

Multidimensional arrays as function parameters

• Similar to one-dimensional array
  • 1st dimension size is not given,
  • 2nd (and 3rd, 4th) dimension are given as constant

void displayPage(const char p[][100], int sizedim1);