Thread: Segmentation Fault

I am new at C, and I made a program to test out my newly acquired knowledge of functions. Here is what the code looks like:

Code:

/* This is to test functions, and hopefully comparitive/logical operators */
main()
{
	char reply;
	int output;
	printf("Do you want to (a)dd or (s)ubtract the numbers 5 and 4?");
	scanf("%c",reply);
	switch (reply) {
	case 'A':
		output = Add();
		break;
	case 'S':
		output = Subtract();
		break;
	default:
		printf("Input Error. Use the letters A or S next time.");
	}
	printf("Done. %d",output);
}

int Add()
{
	int output;
	output=5+4;
	return(output);
}
int Subtract()
{
	int output;
	output=5-4;
	return(output);
}

This code compiles fine, with no errors or warnings. Then, when I run it and type in A or S at the printf statement, it says "Segementation Fault". I have no idea what that means, but I get it a lot on programs. Before, I just gave up, but now it is getting annoying and I want to know what I'm doing incorrectly.

I am using GCC to compile the program, GVIM to program it, and Debian GNU/Linux as my operating system.