Incompatible type error

#include<windows.h>
#include<stdio.h>
#include <ctype.h>
typedef struct ret
{
	long long memory;
	char* drive;
};
int main()
{
	struct ret total_memory;
	total_memory=size_show(GetLogicalDrives());
	return 0;
}
struct ret size_show(long int  n ) 
{
	struct ret to_func;
	long long ii;
	long int  i, k, andmask;
	char a[5]="E://";
	char c;
	printf("%d",strlen(a));
	printf("drives available\n");   
	for ( i = 32 ; i >= 0 ; i-- )  
	{   
		andmask = 1 << i;   
		k = n & andmask;
		if(k!=0)
		{
			k=i+65;
			printf("%c:\n",k);
		}
	}
	printf("drive you want to clear\n");
	scanf("%c",&c);
	a[0]=toupper(c);
	printf("%s.\n",a);
	printf("%d\n",strlen(a));
	i=strcmp("E://",a);
	printf("%d",i);
	k=GetDiskFreeSpaceEx(a,NULL,NULL,&ii);
	printf("%ld",k);
	printf("%ld",ii);
	to_func.memory=ii;
	strcpy(to_func.drive,a);
	return to_func;
}