When would one use ‚ohne..dass and ohne...zu in German? Both translate as without but how are they used?

Question

Answer

You can use "ohne zu" + infinitive if the verb after zu takes the same subject as the main clause. This is a kind of short form that works without repeating the subject.
"Ohne dass" requires a full subordinate clause including a subject. You have to use this if the subject of the subordinate clause is different from the subject in the main clause.

Examples:
Er geht über die Straße ohne sich umzusehen. (The subject of "umzusehen" is also "er")

Er geht über die Straße ohne dass der Autofahrer ihn bemerkt. (Two different subjects: "er" and "der Autofahrer").

You can also transform any "ohne zu" sentence into an "ohne dass" sentence:
Er geht über die Straße ohne dass er sich umsieht. (Notice that "er" occurs twice here).