Currently, you can't create a Formula number field with the 'If, Else' statement. You can only create a formula field using the IF condition. However, you can also achieve the If, Else statement using the If condition.
Let's say you want to make sure that if a check box is enabled, the date field should be populated automatically by filling out next Friday. For example, if you enable the check box today, that date field should be filled with next Friday i.e 16-06-2017. Similarly, if you enable the check box by 17-06-2017, then the date field should be populated with 23-06-2017.
Then, you can define this formula:
If(And(${Deals.checkboxdate},Weekday(Now())==1),Datepart(Adddate(Now(),8,'DAY')),If(And(${Deals.checkboxdate},Weekday(Now())==2),Datepart(Now()),
If(And(${Deals.checkboxdate},Weekday(Now())==3),Datepart(Adddate(Now(),6,'DAY')),If(And(${Deals.checkboxdate},Weekday(Now())==4),Datepart(Adddate(Now(),5,
'DAY')),If(And(${Deals.checkbox date},Weekday(Now())==5),Datepart(Adddate(Now(),4,'DAY')),If(And(${Deals.checkbox date},Weekday(Now())==6),Datepart(Adddate(Now(),3,'DAY')),If(And(${Deals.checkbox date},Weekday(Now())==7),Datepart(Adddate(Now(),2,'DAY')),'')))))))