Pointer arrays and two-dimensional array pointer variables

Pointer Array Concepts:

An array whose element value is a pointer is an array of pointers. A pointer array is a collection of ordered sets of pointers . all elements of a pointer array must be pointer variables that have the same storage type and point to the same data type.

The general form of the pointer array description is:

Type descriptor * array name [ array length ]

Where the type descriptor is the type of the variable to which the pointer value points.

For example:

int *pa[3]

indicates that the PA is an array of pointers, which has three array elements, each of which is a pointer to an integer variable .

1 , using a pointer array to point to a two-dimensional array.

Each element in the pointer array is given the first address of each row of a two-dimensional array, so it can also be understood as pointing to a one-dimensional array.

Example code:

#include<stdio.h> 
main()
{
    int a[3][3]={1,2,3,4,5,6,7,8,9};
    int *pa[3]={a[0],a[1],a[2]};
    int *p=a[0];
    int i;

    for(i=0;i<3;i++)
        printf("%d,%d,%d\n",a[i][2-i],*a[i],*(*(a+i)+i));
    for(i=0;i<3;i++)
        printf("%d,%d,%d\n",*pa[i],p[i],*(p+i));
}In this case, the PA is an array of pointers, and three elements point to the rows of the two-dimensional array, respectively. The specified array element is then output with a looping statement.    *pa[i] represents an i row 0 column element value, because p is the same as a[0], so p[i] represents the value of 0 rows I column, * (P+i) represents the value of the 0 row I column.  int *p[3] indicates that P is an array of pointers, and that there are three subscript variables p[0],p[1],p[2] are pointer variables. 2.pointer arrays represent a set of strings and serve as function argumentsExample code 1:#include <stdio.h>
void Main ()
{
Char *day_name (char *name[],int N);

static char *name[]={"Illegal Day",
"Monday",
"Tuesday",
"Wednesday",
"Thursday",
"Friday",
"Saturday",
"Sunday"
};
Char *ps;
int i;

printf ("Input Day no:\n");
scanf ("%d", &i);

if (i<0)
Exit (1);

Ps=day_name (Name,i);
printf ("Day no:%2d-->%s\n", i,ps);
}

Char *day_name (char *name[],int N)
{
Char *pp1,*pp2;
Pp1=*name;
pp2=* (Name+n);
Return ((n<1| | N&GT;7)? PP1:PP2);
}Example code 2:#include <string.h>
#include <stdio.h>

Main ()
{
void sort (char *name[],int n);
void print (char *name[],int n);
Static char *name[]={"China", "AMERICA", "AUSTRALIA",
"FRANCE", "GERMAN"};
int n=5;
Sort (name,n);
Print (name,n);
}

void sort (char *name[],int N)
{
Char *pt;
int i,j,k;
for (i=0;i<n-1;i++)
{
K=i;
for (j=i+1;j<n;j++)
if (strcmp (Name[k],name[j]) >0)
K=j;
if (k!=i)
{
Pt=name[i];
NAME[I]=NAME[K];
name[k]=pt;
}
}
}

void print (char *name[],int N)
{
int i;
for (i=0;i<n;i++)
printf ("%s\n", Name[i]);
}  Attention should be paid to the difference between pointer arrays and two-dimensional array pointer variables.  Both of these can be used to represent two-dimensional arrays, but their representations and meanings are completely different. Two-dimensional array pointer variable two-dimensional array pointer variable is a single variable, for example int (*p) [4] representsp is a pointer variableA pointer to a one-dimensional array that contains 4 integral elements. int (*p) [4]; Indicates that the *P has 4 elements, and each element is an integer type.The object that P refers to is an array of 4 integral elements, that is, p is a pointer to a one-dimensional array。at this point P can only point to a one-dimensional array containing 4 elements, and the value of P is the starting address of a one-dimensional array.  P cannot point to an element in a one-dimensional array. int a[3][4];    int (*p) [4];    P=a; Since P is a 0-row element that points to a two-dimensional array,so P+i is the start address of the I line of the two-dimensional array a。 * (* (p+2) +3) is the value of a[2][3]. Example code:#include <stdio.h>
void Main ()
{
void average (float *p,int n);
void Search (float (*p) [4],int N);

Float score[3][4]={
{65,67,70,60},
{80,87,90,81},
{90,99,100,98}
};

Average (*score,12); Average of 12 students
Search (score,2); Students with a number 2 are asked to score
}

void average (float *p,int N)
{
float *p_end;
float Sum=0,aver;

p_end=p+n-1;
for (; p<=p_end; p++)
sum+= (*P);
aver=sum/n;

printf ("average=%5.2f \ n", aver);
}

void Search (float (*p) [4],int N)//p is a pointer to a one-dimensional array with 4 elements
{
int i;
printf ("The score of no.%d is: \ n", n);

for (i=0;i<4;i++)
printf ("%5.2f", * (* (p+n) +i));
printf ("\ n");
}

From for notes (Wiz)

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Pointer arrays and two-dimensional array pointer variables