# Two-dimensional array

## Definition

, for example:

float a [3] [4], b [5] [10];

Definition A is an array of 3 * 4 (3 lines 4 columns), B is an array of 5 * 10 (5 lines 10 columns). Note that

float a [3, 4], b [5, 10];

is not easy to understand, a C language program and its operation results:

` #include int main (int Argc, const char * argv []) {int Array [3] [5] = {0}; // Define a two-dimensional array (3 rows 5 columns) int Temp = 0 ; // Set a temporary integer variable to assign a value for the array for (int A = 0; a  operation result is (for easy viewing, finishing into a table):  `
 array [0] [0] = 1 array [0] [1] = 2 < / p> array [0] [2] = 3 array [0] [3] = 4 array [0] [4] = 5 array [1] [0] = 6 array [1] [1] = 7 Array [1] [2] = 8 array [1] [3] = 9 array [1] [4] = 10 array [2] [1] = 12 array [2] [2] = 13 array [2] [3] = 14 < / p> array [2] [4] = 15

## overview

Two-dimensional array a [m] [n], this is a M line, N-column two-dimensional array. Set a [P] [q] for a first element of A, that is, two-dimensional array The subscript from P to M + P, column subscript from q to n + q, press "Row priority order" storage When it is stored, the address of element a [i] [j] is calculated as:

LOC (a [i] [ J]) = LOC (a [p] [q]) + (i - p) * n + (j - q)) * t

When storing by "column priority order", the address is calculated To:

LOC (a [i] [j]) = LOC (a [p] [q]) + ((j - q) * m + (i - p)) * t

Store at least the number of cells required (M-P + 1) * (N-Q + 1) * T by-byte

## Basic operation

### Transposition matrix

// wherein A, B is M * N matrix:

` void track (Matrix A, Matrix B) {INT I, J; for (i = 0; I  matrix phase Add   //) A, B, C is M * N matrix: Void AddMat (Matrix C, Matrix A, Matrix B) {INT I, J; for (i = 0; I  matrix multiplied   // wherein A is M * n matrix, B is N * 1 matrix, C is M * 1 matrix Void Mutmat (Matrix C, Matrix A, Matrix B ) {INT I, J, K; For (i = 0; i  related concept    C ++ dynamic 2D array:    to shaping For example, the ROW is the number of rows, and the COL is the number of numbers   int ** data; // stores a 2D array pointer (pointing to the pointer to the pointer. Date = x [0] [0] of the address. Such a standard is better. Because Sizeof (Date) result is 4 不 不 二 二 数 数 组)   // The following implementation How to apply for a memory Data = new int * [rot]; for (int K = 0; k  // Assignment, for example, DATA [0] [0] = 5; // = 5 = 5 = 5 (called 0 row 0 columns in C ++) to 5 // Delete Memory for (int) i = 0; I  See  matrix    matrix     sparse matrix        `
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