CodeGolf - Heads or Tails

C, 18 bytes

Pretty easy, but let's do it just for fun...

puts("-1"+*i/8%2);

Given the string char *i it prints 1 for heads and -1 for tails, with trailing newline.

Explanation

In C, "-1" + 1 points to 1 character forward, so it is the same as "1". Let's take a look at the first characters:

"heads"[0] = 'h' = 104 = 0b01101000
"tails"[0] = 't' = 116 = 0b01110100

If we count the bits from the rightmost one starting at zero, bit 3 is 1 in heads and 0 in tails: summing it to "-1" gives the right string. It looks like this:

"-1" + ((i[0] >> 3) & 1)

Now, substitute i[0] with *i and the right shift with the power-of-two division to save some bytes. Also remove useless parentheses:

"-1" + (*i / 8 & 1)

Now, & 1 can be substituted with % 2. The character count is the same, but the modulus has higher priority, allowing to drop the parentheses. Remove the whitespace:

"-1"+*i/8%2

Bonus

I think the shortest way to get an integer 1 or -1 (not a string) in C is:

18-*i/6

Explanation:

'h' = 104
't' = 116

('h' + 't') / 2 = 110
110 - 'h' =  6
110 - 't' = -6

(110 - 'h') / 6 =  1
(110 - 't') / 6 = -1

Apply distributive property (integer division):
18 - 'h' / 6 =  1
18 - 't' / 6 = -1

CJam, 4 bytes

I'e#

Assumes that the variable I holds the input, since i isn't a valid identifier in CJam.

Try it online.

This is equivalent to the JavaScript code I.indexOf('e').

Ruby, 8 (6 without output)

p ?t<=>i

Rocketship operator!