Zero conditional

if + present tense | present tense
if + past tense | past tense

The zero conditional expresses that something is (or was) always true or that one action is (or was) always followed by another:

If you heat water to 100 degrees Celsius, it boils.
If John is cursing, it means that he is very angry.

If I got home late, my mom scolded me.
If she was sad, she just stared into the distance without saying a word.

In this type of conditional, we can use when instead of if:

If/When John is cursing, it means that he is very angry.