As far as the compiler is concerned, you only need braces if you want to execute several lines of code contingent on the if. So this is fine:
if(x<0)
x++;
Later, if you decide that something else needs to be executed there, you'll have to remember to add the braces to get more than one statement controlled by the if. To avoid the problems that occur if you forget, many people use braces with every if, whether they are strictly necessary or not.