1. Conditionals without "if" are possible using:
"unless" (means "if not"). It is followed by a verb in the affirmative (Type 1 Conditionals):
1. Unless you give up junk food, you won't lose any weight.
2. Unless there is a lot of traffic, I'll be home soon.
3. Unless it stops snowing, the plain won't take off.
4. Mike will leave Britain soon, unless his grant is extended.
"as/so long as", "providing (that)/provided (that)":
1. You can go out as long as you clean your room.
2. There might be a lot of money in it, providing (that)/provided (that) you go about it the right way.
Note: We use providing (that) usually in speaking. Provided (that) is more common in writing and formal English.
"suppose"/"supposing" - when we talk about a hypothetical condition or situation and then imagining the result:
1. Suppose/supposing you find a wallet with money, what will you do?
2. Suppose/supposing you won a lottery of USD 50,000. How would you spend the money?
"on condition that":
1. We will let you go to the party on condition that you finish your homework.
2. I'll lend you my car on condition that you return it tomorrow.
1. What if you lost your keys? What would you do?
2. What if you get fired from a job for no reason? What will you do?
2. Conditionals without "if" are also possible using inversion. We can omit "if" and use "should" (Type 1 Conditionals), "were" (Type 2 Conditionals) and "had" (Type 3 Conditionals) before the subject. The structure is more common in formal English.
1. If you should need my advice, you can call me.
Should you need my advice, you can call me.
Note: This is similar to "If you need my advice" (without "should"). We can use "should" after "if" when we talk about something possible but not likely to happen.
2. If you should see Tom, please tell him to phone me.
Should you see Tom, please tell him to phone me.
3. If they were to arrive tomorrow, we would be quite unprepared.
Were they to arrive tomorrow, we would be quite unprepared.
Note: We use the structure "were + subject + to-infinitive" when we talk about the imaginary or improbable future situations.
4. If he were more sociable, he would have more friends.
Were he more sociable, he would have more friends.
5. If I hadn't been ill, I would have come.
Had I not been ill, I would have come.
6. If Jason had gone to the party, he would have seen Susan.
Had Jason gone to the party, he would have seen Susann.
See also: Conditionals. Zero, First, Second Conditionals
Conditionals. Third and Mixed Conditionals