Jabo

or better yet

lectricpharaoh

Both of these will yield undefined behavior, as you are modifying the same variable multiple times between sequence points.

In the first case, you are doing two assignments. Since sum += i is shorthand for sum = sum + i, the expression sum = sum += i evaluates to sum = (sum = sum + i). In the second case, remember that the postincrement operator modifies the variable's value, as does the assignment. As the intention is obviously to simply increment the variable's value, using the postincrement alone is sufficient. Furthermore, as the result of the expression is not needed, it's best to use preincrement rather than postincrement:

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DaWei

@Jabo: better for typing? It emits the same code.

@lectric: preincrement on an int is neither better nor worse than post increment. Again, examine the emitted code. For overloaded increment operators, there may be a couple instructions worth of difference.

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Jabo

the difference between post and pre is, pre will increase the variable before using it and post will increment it afterwards. this is only relevant if the variable is being used in another function on the same line. if the increment is by itself, there is absolutely no difference.

say you use the variable in a cout statement, if you say
it will print the value of count before incrementing it
but if you do a preincrement
it will increment the variable before printing it

feel free to correct me if i'm wrong

yes, better for typing, not necessarily better for learning, but since OP already included the statement in his post, I figured he at least knew about it but just didn't understand how to use it.