6. Array

Today’s Outline

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• Array Definition
• Array Initialization
• Passing Arrays to Function
• Array Operations
• Multi-Dimensional Array

Array Definition

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// must be declared with constant integer
int mark[10];
 
// doesn't work
int v;
int mark[v];

Array Initialization

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// Basic Initialization
int a[3] = {1, 2, 3}; // {1, 2, 3}
 
// Initialization without Size
int b[] = {1, 2, 3};  // {1, 2, 3}
 
// Partial Initialization
int c[5] = {1, 2, 3}; // {1, 2, 3, 0, 0}
 
// Initialization to All Zeros
int d[3] = {0};       // {0, 0, 0}

Initialization of Char Arrays

char str[3] = {'a', 'b', 'c'};
char str[3] = "abc";
char str[] = "abc"; // char[4] {'a', 'b', 'c', '\\0'}

Passing Arrays to Function

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void func(int a[]) {
    cout << a[0] << endl; // print 1
    a[0] = 10;
}
 
void main() {
    int a[3] = {1, 2, 5};
    func(a);
    cout << a[0] << endl; // print 10
}

Array Operations

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sizeof

cout << sizeof(int); // 4
int a[4];
cout << sizeof(a);   // 16

Compare two arrays

int main() {
    int array1[5] = {10, 5, 3, 5, 1};
    int array2[5];
    cout << "input 5 elements to array2" << endl;
    for (int i = 0; i < 5; i++) {
        cin >> array2[i];
    }
    bool arrayEqual = true;
    for (int i = 0; i < 5 && arrayEqual; i++) {
        if (array1[i] != array2[i]) {
            arrayEqual = false;
        }
    }
    if (arrayEqual) {
        cout << "The arrays are equal" << endl;
    } else {
        cout << "The arrays are not equal" << endl;
    }
    return 0;
}

Sort

• Slow but easy to code
  • Selection sort
  • Bubble sort
  • Insertion sort
• Faster but more complex to code
  • Quick sort
  • Merge sort
  • Heap sort

Search

• Binary Search

Multi-Dimensional Array

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• Array with more than one index
• Stored in the row-major order

2D Array Initialization

int page[2][3] = {{1,2,3},{4,5,6}};
int page[2][3] = {1,2,3,4,5,6};
int page[2][3] = {{1},{4,5}}; = {{1,0,0},{4,5,0}}
int page[][3] = {1,2,3,4,5,6};
int page[2][] = {1,2,3,4,5,6}; // compile error

Passing 2D Array to Function

void sort2D(int x[][10]) { // 1st dimension is optional, 2nd must be given
    // ...
}
 
void main() {
    int y[20][10];
    sort2D(y);
}