C-String problem

[syzn]

Can someone help me figure out what I am doing wrong here? I keep getting this error after I input:

Unhandled exception at 0x54AE350B (msvcp110d.dll) in Random.exe: 0xC0000005: Access violation writing location 0x0131CA21.

The code:

#include <iostream>
#include <cstring>

//Prototypes
void lastChar(char *);

int main()
{
	const int LENGTH = 21;
	char *input = "";

	std::cin.getline(input, LENGTH);
	lastChar(input);

	return 0;
}

void lastChar(char *str)
{
	for(unsigned int count = 0; count < strlen(str); count++)
	{
		if(str[count] == '\0')
		{
			std::cout << str[count-1];
		}
		else
		{
			str++;
		}
	}
}

It builds without any errors. I am just trying to output the last character in the C-string. Am I doing this all wrong? D: