“C”为什么我将变量声明为“指针”？

Question

#include <stdio.h>
void main()
{
int a[] = {10,20,30,40,50,60,70,80,90,100};
int k,m,i,*ptr;
k=m=0;
ptr=a;
for(i=0; i<10; i+=2)
{
    k+=ptr[i];
    m+=ptr[i+1];
}
printf("***** result ***** \n\n");
printf("(10+30+50+70+90)=%d\n",k); //250
printf("(20+40+60+80+100)=%d\n",m); //300
}

Why I use the *ptr as 'pointer'? I mean it cannot run using just 'ptr'?

How the variable '*ptr' load the array 'a[]'.

Answer 1

Here the pointer ptr points to the first element of the array. If you declared it as a regular variable, you could only assign one value to it. But now you can assign the address of an array element & access all other elements through it by incrementing or decrementing the value of the pointer, which you won't be able to do, if it was declared as a variable.

The pointer ptr points to the first element of the array. So if you write ptr[1], it points to the second element of the array (since arrays are '0'-indexed). You can access other elements too.