I was wondering if there was a difference between =+ and += (and other assignment operators too). I tried and both did the same thing. So is there a difference or is there a convention? Do both work because my compilers dont check for standarts?
Edit: I made a mistake. I used bad inputs during my testing which led me to thinking they are both doing the same thing. Turns out they are two different things.
+= adds rvalue to lvalue
x += y;
x = x + y;
=+ assigns rvalue to lvalue
x =+ y;
x = +y;
x = y;
In modern C, or even moderately ancient C, += is a compound assignment operator, and =+ is parsed as two separate tokens. = and +. Punctuation tokens are allowed to be adjacent.
So if you write:
x += y;
it's equivalent to
x = x + y;
except that x is only evaluated once (which can matter if it's a more complicated expression).
If you write:
x =+ y;
then it's parsed as
x = + y;
and the + is a unary plus operator.
Very early versions of C (around the mid 1970s, before the publication of K&R1 in 1978) used different symbols for compound assignments. Where modern C uses +=, early C used =+. Early C had no unary + operator, but it did have a unary - operator, and the use of =- caused problems; programmers would write x=-y intending it to mean x = -y, but it was silently interpreted as x =- y. The language was changed some time between 1975 and 1978 to avoid that problem. As late as 1999, I worked with a compiler (VAXC on VMS) that would warn about an ambiguous use of =-, but would use the older meaning. That shouldn't be a concern now unless you're a hobbyist playing with some very old software and/or hardware.
(A 1975 C Reference Manual shows the old =-, =+, et al forms of the compound assignment operators. The first edition of The C Programming Language by Kernighan and Ritchie, published in 1978, shows the modern -=, +=, et al, but mentions the older forms under "Anachronisms".)