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Questions tagged [compound-assignment]

For questions about single operators that assign a value based on both a previous value and an operand (e.g., the += operator in C or Python). Also referred to as "augmented assignment." Use this tag if your problem specifically involves or relates to a compound-assignment operator.

Compound assignment operators, such as +=, combine aspects of assignment with aspects of regular binary operators. For example, i += 42 generally has the effect of i = i + 42, but is more concise.

However, that is not always the case. For example, in a Python 3 class, a custom + can be implemented using the __add__ method, and a custom += can be implemented using the __iadd__ method. Those two methods could behave very differently.

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How can you use compound assignment operators in C if you can't redefine variables?

Looking at wikipedia it says: a -= b; is the same as a = a - b; But when I try this in my C program I get the following error: "error: redefinition of 'a'". Here is my program: #include int main(int argc, char *argv[]) { int a =…
CClarke
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Concern with the vocabulary of JLS

I always see this strange symbol § but never understand wtf means Also what E1, T, op means here? From the post: Why don't Java's +=, -=, *=, /= compound assignment operators require casting? Correct me: T = data type op = operator
Pablo_06
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Confusion about compound assingnments (+=, -=, *=, ...) in Java

I'm a little confused about the result of the following code: int x = 1; x -= ((x += 1) << 1); System.out.println(x); It prints out -3, but I'd expected it to print out -2, because in my head the computation should go like this: |…
txmns
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+= in Python when assigning it to third variable

When I was looking at meaning of the += operator in Python, I looked at the answers to a similar question: What exactly does += do in python?. But in the below code excerpt: increments += arr[i-1] - arr[i] There is a third variable used. If I…
Sreedhar Danturthi
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c compound assignment increment only right bits

I am new to C and working with a serial device and I have this line: short DA, DacData; DA=0xFFF; DacData = ((channel&0x03)<<14)|((serialA&0x03)<<12)|(DA&0x6AA); How do I increment only the last part of DacData (DA&0x6AA) in my loop? Thanks in…
Takuzo Kimura
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Better way to write 'assign A or if not possible - B'

So, in my code I have a dictionary I use to count up items I have no prior knowledge of: if a_thing not in my_dict: my_dict[a_thing] = 0 else: my_dict[a_thing] += 1 Obviously, I can't increment an entry of a value that doesn't exist yet.…
Sanuuu
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Optimizing repeating assignment of variable values

In an effort to learn compound assignment in C++, I created the following code to demonstrate what they do: int b05; int b06 = 13; b05 = 49; b05 += b06; // b05 = b05 + b06 cout << "(+=) compound assignment: " << b05 << endl; b05 = 49; b05 -= b06;…
James E. Prater
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How does the or-assignment operator (|=) work? (C#)

I've seen documentation and answers (1) (2) that try to explain what the |= operator is and how it works, and while it kind of makes sense on a basic level... I don't quite get why or how it accomplishes what it does. The explanations say that a |=…
JaykeBird
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c++ presedence of operators

Hi guys so I need some help understanding how these compound assignment operators work for example int x=6; x += x -= x * x; x turns out to be -60 can someone explain why and how this works?
CanyoucSharp
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Isn't parameter type of function like "string& operator+= (const string& str)" confusing? (reference to const)

string& operator+= (const string& str); When we look at the function prototype, we assume that the string passed into the function won't be changed, right? However, consider the situation: string str("Example"); str += str; The string 'str' was…
Jann Cooky
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JavaScript run calculation after radio button checked

New to JavaScript and can't get my head around this exercise: Need to modify JavaScript so it provides for the option buttons. When the user selects yearly interest rate button, the application should compound the yearly rate and when the user…
Miss Juhasz
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How to hold a const value in a struct in C (not C++)?

How can I hold a constant value in a struct? If I put const at LEBEL0 I would not be able to assign to it at LEBEL1. But if I do not put const at LEBEL0, then I will get qualifier lost warning at LEBEL1. Is there any way to do this? I came up with a…
Damn Vegetables
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BlueJ Java compound condition

im currently doing some code and am having problem and cant get my head around it. I am very new at this is any help would be appreciated I'm trying to make a compound condition for the date but cant seem to understand how to do it. public void…
user3113362
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Using the result of compound assignment as an lvalue

I'm surprised that this works: double x = 3; double y = 2; (x *= 2) += y; std::cout << x << std::endl; The result is 8, which is what it looks like the programmer is trying to achieve. But I thought assignment operators returned an rvalue - how…
Tom
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What is the meaning and name for "+=" in C++?

I am fairly new to C++ and I have been reading and writing some of my own code. I see these operators from time to time, if that is even the right word to use? += // Not sure what it means So my question is: what do they mean/do, and what are they…
dusz
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