C language: 5. Multidimensional array

Article reference ：https://wangdoc.com/clang/array.html

1、 Define array format

 data type    Array name [ length 1][ length 2]...[ length n]

int num[3][3] = {
    {
    1,2,3}, {
    1,2,3}, {
    1,2,3}};

Think of the above array as a 3x3 Matrix , Here's the picture ：

2、 Initialize array mode

The way 1：

 data type    Array name [ length 1][ length 2]...[ length n] = {
   { value 1,...,  value n},...{ value 1, ...,  value n}};

The way 2：

 data type    Array name [ length 1][ length 2]...[ length n];
 Array name [ Subscript 1]...[ Subscript n] =  value ;

Be careful ：
Adopted by 1 When initializing an array , The dimension of the column must be specified , Because the system allocates space according to the total number of elements in the array , When you know the total number of elements and the dimension of the column , The dimension of travel will be calculated directly .
When using the second initialization , Arrays must specify both row and column dimensions .

#include <stdio.h>
int main()
{
    
    // Use the first method to declare and initialize a two-dimensional array arr1
    int arr1[][3] = {
    {
    1,2,3},{
    1,2,3},{
    1,2,3}};
    // Use the second method to declare and initialize the two-dimensional array arr2
    int arr2[3][3];
    return 0;    
}

3、 Arrays as function arguments

because C The language has no way to get the length of an array , Therefore, array length is generally required to be passed in as a parameter

3.1、 One dimensional array as parameter

int ArraySum(int array[], int length){
    
    int sum = 0;
    for(int i=0; i<length; i++){
    
        sum += array[i];
    }
    return sum;
}
int main(){
    
    int array[] = {
    1,2,3};
    int sum = ArraySum(array,3);
    return 0;
}

3.2、 Multidimensional array as parameter

Multidimensional array as parameter , In addition to the first dimension, the array length can be passed with parameters , Others need to be defined

int sumArray(int array[][4], int length){
    
    int sum = 0;
    for(int i=0; i<length; i++){
    
        for(int j=0; j<4; j++){
    
            sum += array[i][j];
        }
    }
    return sum;
}
int arr[4][4] = {
     {
    1,2,3,4}, {
    1,2,3,4}, {
    1,2,3,4}, {
    1,2,3,4}, };
int sumNo = sumArray(arr,4);

n Dimension group as parameter

int sumMulArr(int array[][3][3], int length){
    
    // ...
    return 0;
}

3.3、 Variable length array as parameter

The length of the array in the following example depends on the parameter length, Only the runtime knows , So parameters length The position of must be in the parameter array front , Otherwise, an error will be reported

void SumArray(int length, int array[length]){
    
    //...
}

Because the function prototype can omit the parameter name , So in the prototype of variable length array , have access to * Instead of the variable name , You can also omit the variable name .

int SumArray(int, int [*]);
int SumArray(int, int []);

3.4、 Array literal as a parameter

// Array variables as parameters 
int a[] = {
    2,3,4,5};
int sum = sum_array(a, 4);

// Array literal as a parameter 
int sum = sum_array((int []){
    2,3,4,5}, 4);

In the above example , The two expressions are equivalent . The second method omits the declaration of array variables , Directly pass the array literal into the function ,{2,3,4,5} Is the literal value of the array ,(int []) Similar to forced type conversion , Tell the compiler how to understand this set of values