pre-increment

Multiple preincrement operations on a variable in C++(C ?)

由 给你一囗甜甜゛ 提交于 2019-11-26 07:35:44
问题 Why does the following compile in C++? int phew = 53; ++++++++++phew ; The same code fails in C, why? 回答1: That is because in C++ pre-increment operator returns an lvalue and it requires its operand to be an lvalue . ++++++++++phew ; in interpreted as ++(++(++(++(++phew)))) However your code invokes Undefined Behaviour because you are trying to modify the value of phew more than once between two sequence points. In C , pre-increment operator returns an rvalue and requires its operand to be an

Incrementor logic

由 北慕城南 提交于 2019-11-26 06:38:15
问题 I\'m trying to get deeper with post and pre incrementors but am a bit stuck with the following expression : public static void main(String[] args) { int i = 0; i = i+=(++i + (i+=2 + --i) - ++i); // i = 0 + (++i + (i+=2 + --i) - ++i); // i = 0 + (1 + (3 + 2) - 1); // i = 0 + (6 - 1); System.out.println(i); // Prints 0 instead of 5 } I know I\'m missing the logic somewhere but where? What I\'ve tried : Going from left to right (though I know it is not recommended) Going from the insidest

Order of operations for pre-increment and post-increment in a function argument? [duplicate]

由 让人想犯罪 __ 提交于 2019-11-26 05:36:20
问题 This question already has answers here : Why are these constructs using pre and post-increment undefined behavior? (14 answers) Closed last year . I have some C code: main() { int a=1; void xyz(int,int); xyz(++a,a++); //which Unary Operator is executed first, ++a or a++? printf(\"%d\",a); } void xyz(int x,int y) { printf(\"\\n%d %d\",x,y); } The function xyz has two parameters passed in, ++a and a++ . Can someone explain the sequence of operations to explain the result? The above code prints

Difference between pre-increment and post-increment in a loop?

由 孤人 提交于 2019-11-26 01:18:58
问题 Is there a difference in ++i and i++ in a for loop? Is it simply a syntax thing? 回答1: a++ is known as postfix. add 1 to a, returns the old value. ++a is known as prefix. add 1 to a, returns the new value. C#: string[] items = {"a","b","c","d"}; int i = 0; foreach (string item in items) { Console.WriteLine(++i); } Console.WriteLine(""); i = 0; foreach (string item in items) { Console.WriteLine(i++); } Output: 1 2 3 4 0 1 2 3 foreach and while loops depend on which increment type you use. With

Incrementing in C++ - When to use x++ or ++x?

由 元气小坏坏 提交于 2019-11-26 00:58:21
问题 I\'m currently learning C++ and I\'ve learned about the incrementation a while ago. I know that you can use \"++x\" to make the incrementation before and \"x++\" to do it after. Still, I really don\'t know when to use either of the two... I\'ve never really used \"++x\" and things always worked fine so far - so, when should I use it? Example: In a for loop, when is it preferable to use \"++x\"? Also, could someone explain exactly how the different incrementations (or decrementations) work? I

Incrementing in C++ - When to use x++ or ++x?

由 点点圈 提交于 2019-11-26 00:47:29
I'm currently learning C++ and I've learned about the incrementation a while ago. I know that you can use "++x" to make the incrementation before and "x++" to do it after. Still, I really don't know when to use either of the two... I've never really used "++x" and things always worked fine so far - so, when should I use it? Example: In a for loop, when is it preferable to use "++x"? Also, could someone explain exactly how the different incrementations (or decrementations) work? I would really appreciate it. It's not a question of preference, but of logic. x++ increments the value of variable x

Is there a performance difference between i++ and ++i in C?

由 怎甘沉沦 提交于 2019-11-26 00:14:54
问题 Is there a performance difference between i++ and ++i if the resulting value is not used? 回答1: Executive summary: No. i++ could potentially be slower than ++i , since the old value of i might need to be saved for later use, but in practice all modern compilers will optimize this away. We can demonstrate this by looking at the code for this function, both with ++i and i++ . $ cat i++.c extern void g(int i); void f() { int i; for (i = 0; i < 100; i++) g(i); } The files are the same, except for

Java: Prefix/postfix of increment/decrement operators?

由 ▼魔方 西西 提交于 2019-11-26 00:07:05
问题 From the program below or here, why does the last call to System.out.println(i) print the value 7 ? class PrePostDemo { public static void main(String[] args){ int i = 3; i++; System.out.println(i); // \"4\" ++i; System.out.println(i); // \"5\" System.out.println(++i); // \"6\" System.out.println(i++); // \"6\" System.out.println(i); // \"7\" } } 回答1: i = 5; System.out.println(++i); //6 This prints out "6" because it takes i adds one to it and returns the value. 5+1=6; This is prefixing,

Is there a performance difference between i++ and ++i in C++?

由 心不动则不痛 提交于 2019-11-25 22:56:50
问题 We have the question is there a performance difference between i++ and ++i in C? What\'s the answer for C++? 回答1: [Executive Summary: Use ++i if you don't have a specific reason to use i++ .] For C++, the answer is a bit more complicated. If i is a simple type (not an instance of a C++ class), then the answer given for C ("No there is no performance difference") holds, since the compiler is generating the code. However, if i is an instance of a C++ class, then i++ and ++i are making calls to

C: What is the difference between ++i and i++?

由 こ雲淡風輕ζ 提交于 2019-11-25 22:55:29
问题 In C, what is the difference between using ++i and i++ , and which should be used in the incrementation block of a for loop? 回答1: ++i will increment the value of i , and then return the incremented value. i = 1; j = ++i; (i is 2, j is 2) i++ will increment the value of i , but return the original value that i held before being incremented. i = 1; j = i++; (i is 2, j is 1) For a for loop, either works. ++i seems more common, perhaps because that is what is used in K&R. In any case, follow the
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