what is difference between ++i and i+=1 from any point of view

Question

This is a question from kn king\'s c programming : a modern approach. I can\'t understand the solution given by him:-

The expression ++i is equivalent to (i          


        

Answer 1

Difference between both are: ++ is a unary operator while + is a binary operator.... If we consider execution time: i++ is more faster than i=i+1. No of machine cycles differs to execute the same set of code, thats the reason ++ operators are always prefered for Loops. Refer to this thread for more info

Answer 2

I think they are totally the same. There is one thing maybe interesting. The ++i is equal to (i+=1) but not i+=1; The difference is the brace. Because i += 1 may depend on the context and it will have different interpretation.

Answer 3

In a normal operation without assignation:

++i and i++

increase the variable in 1. In pseudo assembly both code it is:

inc i

but If you assign the value the order of ++ is relevant:

x = i++

produce:

mov x, i
inc i

x = ++i

produce:

inc i
mov x, i

In the case of: i += 1

it will produce:

add i,1

but because compilers optimize the code it also will produce in this case:

inc i

Answer 4

i = 10
printf("%d", i++);

will print 10, where as

printf("%d", ++i);

will print 11

X = i++ can be thought as this

X = i
i = i + 1

where as X = ++i is

i = i + 1
X = i

so,

printf ("%d", ++i); 

is same as

printf ("%d", i += 1);

but not

printf ("%d", i++);

although value of i after any of these three statements will be the same.

Answer 5

One difference that has not been brought up so far is readability of code. A large part of loops use increment by one and common practice is to use i++/++i when moving to the next element / incrementing an index by 1.

Typically i+= is used in these cases only when the increment is something other than 1. Using this for the normal increment will not be dangerous but cause a slight bump in the understanding and make the code look unusual.

Answer 6

The solution means to say that there is no difference, ++i has the same meaning as (i += 1) no matter what i happens to be and no matter the context of the expression. The parentheses around i += 1 make sure that the equivalence holds even when the context contains further arithmetics, such as ++i * 3 being equivalent to (i += 1) * 3, but not to i += 1 * 3 (which is equivalent to i += 3).

The same would not apply to i++, which has the same side effect (incrementing i), but a different value in the surrounding expression — the value of i before being incremented.