Two-dimensional array & pointer

Introduction: Two-dimensional arrays are stored in the form of one-dimensional arrays in memory, so two-dimensional arrays can be regarded as composed of several one-dimensional arrays.

1. Row address & column address

? Line address:

a ↔ & a [0] ( point to line 0 )

a + i ↔ & a [i] ( Direction line i )

? Column address:

a [0] ↔ & a [0] [0] ( point to row 0, column 0 )

a [0] + i ↔ & a [0] [i] ( Direction 0th row, ith column )

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2, the row address? Column address

• The row address points to a row of elements (a one-dimensional array)
• The column address points to an element

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3. The relationship between one-dimensional array and two-dimensional array

The address of the one-dimensional array ↔ the row pointer of the two-dimensional array, pointing to the elements of the row, such as & a [i] ↔ a + i

Elements of one-dimensional array ↔ Row array name of two-dimensional array, pointing to the first element of the row, such as a [i] ↔ & a [i] [0]

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4、a?a[0]

a is the name of the two-dimensional array, the row pointer, increment by 1 to point to the next row

a [0] is the name of the row array, column pointer, incremented by 1 to point to the next column

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? Line pointer

① Definition: int (* p) [4]; ( defines a pointer variable to point to an integer array containing 4 elements )

②Initialization: p = a; or p = & a [0];

③Quote

地址&a[i][j]→ *(p+i)+j​

元素a[i][j]→ p[i][j] ↔ * (p[i]+j) ↔ * (* (p+i)+j) ↔ (*(p+i))[j]

? Column pointer

① Definition: int * p; (Take two-dimensional array as one-dimensional array with m rows and n columns)

②Initialization: p = * a; or p = a [0]; or p = & a [0] [0];

③Quote

地址&a[i][j] → &p[i*n+j]​

元素a[i][j] → p[i* n+j] ↔ * (p+i*n+j)

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Example: input a 2D array with 3 rows and 4 columns and output

Method 1-Two-dimensional array as parameter

#include <stdio.h>
#define N 4
void InputArray(int p[][N], int m, int n);  
void OutputArray(int p[][N], int m, int n);  

int main()
{ 
	int  a[3][4];
	printf("Input 3*4 numbers:\n");                             
	InputArray(a, 3, 4);   /* 向函数传递二维数组的第0行的地址 */                      
	OutputArray(a, 3, 4);  /* 向函数传递二维数组的第0行的地址 */
	return 0;
}
/* 形参声明为列数已知的二维数组，输入数组元素值 */
void InputArray(int p[][N], int m, int n) 
{	
	int i, j;
	for(i = 0; i<m; i++)
		for(j = 0; j<n; j++)
			scanf("%d", &p[i][j]);         
}
/* 形参声明为列数已知的二维数组，输出数组元素值 */
void OutputArray(int p[][N], int m, int n)
{
	int i, j;
	for(i = 0; i<m; i++)
	{ 
		for(j = 0; j<n; j++)
			printf("%4d", p[i][j]); 
			        
		printf("\n");
	}
}

Method 2-Line pointer as a formal parameter

#include <stdio.h>
#define N 4
void InputArray(int (*p)[N], int m, int n);  
void OutputArray(int (*p)[N], int m, int n);  

int main()
{ 
	int  a[3][4];
	printf("Input 3*4 numbers:\n");                             
	InputArray(a, 3, 4);   /* 向函数传递二维数组的第0行的地址 */                      
	OutputArray(a, 3, 4);  /* 向函数传递二维数组的第0行的地址 */
	return 0;
}

/* 形参声明为指向列数已知的二维数组的行指针，输入数组元素值 */
void InputArray(int (*p)[N], int m, int n)   
{	
	int i, j;
	for(i = 0; i<m; i++)
		for(j = 0; j<n; j++)
			scanf("%d", *(p+i)+j);         	
}
/* 形参声明为指向列数已知的二维数组的行指针，输出数组元素值 */
void OutputArray(int (*p)[N], int m, int n)
{
	int i, j;
	for(i = 0; i<m; i++)
	{ 
		for(j = 0; j<n; j++)
			printf("%4d", *(*(p+i)+j));  
		       
		printf("\n");
	}
}

Method 3-Column pointer as a formal parameter (recommended, the number of two-dimensional columns is dynamically variable)

#include <stdio.h>
void InputArray(int *p, int m, int n);  
void OutputArray(int *p, int m, int n);  

int main()
{ 
	int  a[3][4];
	printf("Input 3*4 numbers:\n");
	InputArray(*a, 3, 4);   /* 向函数传递二维数组的第0行第0列的地址 */                      
	OutputArray(*a, 3, 4);  /* 向函数传递二维数组的第0行第0列的地址 */   
	return 0;
}
/* 形参声明为指向二维数组的列指针，输入数组元素值 */
void InputArray(int *p, int m, int n)   
{	
	int i, j;
	for(i = 0; i<m; i++)
		for(j = 0; j<n; j++)
			scanf("%d", &p[i*n+j]);         
}
/* 形参声明为指向二维数组的列指针，输出数组元素值 */
void OutputArray(int *p, int m, int n)
{
	int i, j;
	for(i = 0; i<m; i++)
	{ 
		for(j = 0; j<n; j++)
			printf("%4d", p[i*n+j]);         
		
		printf("\n");
	}
}