Array - C P P

• Array
• Character Array
• 2D Array
• Dynamic Allocation

Array

• An Array is a data structure used to store blocks of information in contiguous memory allocation of same data type
• Subarray
• Subsequence
  • dataType A[N] => Declare an Array of size "N"
    • Giving a Aiable size in an array is a bad practice, as memory is given at run-time in stack
    • Size should be known at compile-time, as size required in run-time may be bigger than capacity of stack
  • dataType A[2] = {value1, value2} => Initialize an Array of size "n" with "n" value
  • dataType A[5] = {value1, value2} => Initialize an Array of size "n" with first "n" value, Rest will be initialized by "0"
  • dataType A[] = {value1, value2, value3} => Initialize an Array with "n" value
  • dataType A[n] = {} => Initialize an Array of size "n" with all value equal to "0"
  • dataType A[n] = {0} => Initialize an Array of size "n" with all value equal to "0", For any value other than "0" can use loops
  • fill_n (A, n, value); = {0} => Initialize an Array till first "n" elements with all value equal to "value"
  • next_permutation(n, m) => Returns next lexicographically greater value for given array of value, Parameter "n" is starting and "m" is ending index
  • functionName(A) => When calling a function, we send the starting address of the array, Value will get changed in the array if updated in function
• STL Commands
  • #include<array> => Library to include
    • Generally takes O(1) time complexity
  • array<int, n> A = {value1, value2} => Initialize
  • A.size() => Returns size of array
  • A.at(n) => Returns value at nth position
    • A[n] => Returns value at nth position
  • A.empty() => Returns boolean value true is array is empty
  • A.front() => Returns first element of the array
  • A.back() => Returns last element of the array
• Loops
  • For Loop

        for (int i = 0; i < arraySize; ++i) {
            cout << A[i] << " ";
        }
    

  • Range-based

        for(auto i: A) {
            cout << A[i] << " ";
        }
    

  • For Each

        for_each(A, A + arraySize, [](int i) {
            cout << A[i] << " ";
        });
    

  • Iterator

        for(auto itr = begin(A); itr != end(A); ++itr) {
            cout << *itr << endl;
        }
    

Character Array

• char A[N] => Declaring a character array
• char* A[3] = {"value1", "value2", "value3"}
• string A[3] = {"value1", "value2", "value3"}
• char A[3][10] = {"value1", "value2", "value3"}
• array<string> A{"value1", "value2", "value3"};
• vector<string> A{"value1", "value2", "value3"};
• cin >> A; => Taking input
  • Adds a null character /0 just like string in the end, Used as a terminator
  • Stops execution when given a newline/space/tab

2D Array

• Mapping 2D array to 1D array
  • Index of 1D = col * i + j = = Total Column * Row + Column
  • Row index in 2D = i/col
  • Col index in 2D = i % col
• We need to specify the column size when passing a 2D array as a parameter
  • void func(int A[][N]) {} => To be able to calculate the element by pointer
    • A[2][3] = *(&A[0][0] + 2*N + 3)
  • *(A + i*cols + j) => Use pointers instead
• Commands
  • dataType A[n][m] => Declaring an 2D Array of n row and m column
  • dataType A[n][m] = {{value1}, {value2}} => Initialize an 2D Array
  • dataType A[n][m] = {value1, value2, value3, value4} => Initialize an 2D Array Row-wise
  • cin >> A[n][m] => Taking input
  • cout << A[n][m] => Getting output of nth row and mth column
• Loops
  • For Loop

        for (int i = 0; i < R; ++i) {
            for (int j = 0; j < C; ++j) {
                cout << A[i][j] << " ";
            }
        }
    

  • Range-based

        for (auto &row: A) {
            for (auto i: row) {
                cout << i << " ";
            }
            cout << endl;
        }