Zero conditional

THE ZERO CONDITIONAL

We can make a zero conditional sentence with two present simple verbs (one in the 'if clause' and one in the 'main clause'):

If/When + present simple (CONDITION), present simple (RESULT). 

This conditional is used when the result will always happen. So, if water reaches 100 degrees, it always boils. It's a fact. I'm talking in general, not about one particular situation. The result of the 'if clause' is always the main clause. 

The 'if' in this conditional can usually be replaced by 'when' without changing the meaning.

For example: 

If water reaches 100 degrees, it boils. (It is always true, there can't be a different result sometimes). 

If I eat shrimp, I am sick. (This is true only for me, maybe, not for everyone, but it's still true that I'm sick every time I eat shrimp)

Here are some more examples:

If/When you heat ice, it melts. 

If/When it rains, I stay at home. 

If/When people eat too much, they get fat. 

People die if/when they don’t eat. 

Snakes bite if/when they are scared. 

If/When babies are hungry, they cry.