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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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Why doesn't compound assignment in Java catch overflow problems?

To my shock, it turns out that the following code will compile without even warnings: public void test() { int value = 2000000000; long increment = 1000000000; value += increment; } Whereas this gives a compile-time error, as you would…
Hakanai
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Are there sequence points in the expression a^=b^=a^=b, or is it undefined?

The allegedly "clever" (but actually inefficient) way of swapping two integer variables, instead of using temporary storage, often involves this line: int a = 10; int b = 42; a ^= b ^= a ^= b; /*Here*/ printf("a=%d, b=%d\n", a, b); But I'm…
Medinoc
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Is i += ++i undefined behavior in C++0x?

I'm very convinced with the explanation I've found that said that i = ++i is not undefined as far as C++0x is concerned, but I'm unable to judge whether the behavior of i += ++i is well-defined or not. Any takers?
Saurabh Manchanda
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What does "|=" operation mean in C++?

I have the following code and I can't understand what does it mean: var1 |= var2>0 ? 1 : 2; Anyone can help me please!
Reem
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What is the difference between += and =+ C assignment operators

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…
Michael
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Auto-(un)boxing fail for compound assignment

Thanks to the implicit casting in compound assignments and increment/decrement operators, the following compiles: byte b = 0; ++b; b++; --b; b--; b += b -= b *= b /= b %= b; b <<= b >>= b >>>= b; b |= b &= b ^= b; And thanks to auto-boxing and…
polygenelubricants
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Purpose of subsequent use of OR and AND compound assignment operators on registers

In C and C++ code, in particular that for embedded systems, I regularly stumble upon assignments that take the following shape: A |= B; A &= B; Not sure if relevant, but A and B are registers here. See an example…
JJM Driessen
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Assigning using += gives NaN in javascript

Assignment a number to an attribute using the += operator gives me NaN in JavaScript. This code works as expected: > var result = {}; undefined > result['value'] = 10; 10 > result['value'] += 10; 20 But here we get NaN: > var test = {}; undefined >…
jsbisht
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ObjC properties and C operators

Given the following property declaration: @property NSInteger foo; How do the increment, decrement, and compound assignment operators actually work on self.foo? It was my understanding that self.foo was merely syntactic sugar for the actual…
nhgrif
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Why does the compound assignment of a string and an int work, but the assignment of a string to a string + int doesn't in C++?

I'm learning C++ and I ran into an interesting predicament that I don't quite understand. My goal is to concatenate a string with the char representation of an int value, say 'a'. My problem is that: string a = "bo"; a = a + 97; Doesn't work,…
Lawrence Hoerst
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How is A *= B *= A *= B evaluated?

public static void main(String[] args) { int A=5; int B=2; A *= B*= A *= B ; System.out.println(A); System.out.println(B); } When I calculated this problem on paper I found A=200 B=20, but when I write it down to eclipse it…
tarikyaylagul
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Compound assignment operators, what happens if the value is modified (in the meanwhile)?

Consider the following pseudocode (language agnostic): int f(reference int y) { y++; return 2; } int v = 1; v += f(v); When the function f changes y (that is v) while evaluating v += f(v), is the original value of v "frozen" and changes to…
gremo
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Is there a compound assignment operator for a = b a (where is not commutative)?

In a lot of languages a = a + b can be written as a += b In case of numerical operations, a + b is same as b + a, so the single compound operator suffices. Also, a = a - b can be written as a -=b . However, a-b is not equal to b-a. Hence, the…
asheeshr
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Using multiple compound assignments in a single expression

I am preparing for a Java exam and I am trying to understand operator precedence and compound assignment operators in depth. I played around with a few expressions which use compound assignment during the evaluation of an expression. However, I do…
Rauni Lillemets
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Difference between tensor addition assignment and assignment in pytorch

I found that pytorch treats tensor assignment and addition assignment differently. Examples are shown below x = torch.tensor(3.0) print(id(x)) x = x + 5 print(id(x)) The results are 1647247869184 1647248066816 If we run the following code x =…
Andy
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