C语言数组a[i]==i[a]

The C standard defines the [] operator as follows:

a[b] == *(a + b)

Therefore a[5] will evaluate to:

*(a + 5)

and 5[a] will evaluate to:

*(5 + a)

and from elementary school math we know those are equal.

This is the direct artifact of arrays behaving as pointers, “a” is a memory address. “a[5]” is the value that’s 5 elements further from “a”. The address of this element is “a + 5″. This is equal to offset “a” from “5” elements at the beginning of the address
space (5 + a).

#include <stdio.h>	

int main()
{
	int a[10]={9,2,3,4,7,6,5,8,1,10};
	//a[b]=*(a+b)
	printf("%d\n",a[5]);
	printf("%d\n",*(a+5));
	printf("%d\n",*(5+a));
	printf("%d\n",5[a]);

	return 0;
}