Menu
I've noticed on a number of occasions when refactoring various pieces of C and C++ code that a comma is used rather than a semi-colon to seperate statements. Something like this;
int a = 0, b = 0; a = 5, b = 5; Where I would have expected
int a = 0, b = 0; a = 5; b = 5; I know that C and C++ allow use of commas to seperate statements (notably loop headers), but what is the difference if any between these two pieces of code? My guess is that the comma has been left in as the result of cut & pasting, but is it a bug and does it effect execution?
507
The comma operator in c comes with the lowest precedence in the C language. The comma operator is basically a binary operator that initially operates the first available operand, discards the obtained result from it, evaluates the operands present after this, and then returns the result/value accordingly.
Rule to Remember Use a semicolon to replace a comma when you use a coordinating conjunction to link independent clauses that already contain commas. In this example, using a semicolon makes it easier to read the two independent clauses on either side of the coordinating conjunction: Correct: My dog is sick.
When a comma separates two complete sentences joined by a conjunction (and, but, or, nor, for, so, or yet) the comma and the conjunction can be replaced with a semicolon. I ate dinner, and I went to the movies. = I ate dinner; I went to the movies. She finished top of her class, but she was struggling to find work.
Semicolons are end statements in C. The Semicolon tells that the current statement has been terminated and other statements following are new statements. Usage of Semicolon in C will remove ambiguity and confusion while looking at the code.
It doesn't make a difference in the code you posted. In general, the comma separates expressions just like a semicolon, however, if you take the whole as an expression, then the comma operator means that the expression evaluates to the last argument.
Here's an example:
b = (3, 5); Will evaluate 3, then 5 and assign the latter to b. So b = 5. Note that the brackets are important here:
b = 3, 5; Will evaluate b = 3, then 5 and the result of the whole expression is 5, nevertheless b == 3.
The comma operator is especially helpful in for-loops when your iterator code is not a simple i++, but you need to do multiple commands. In that case a semicolon doesn't work well with the for-loop syntax.
99
The comma is a operator that returns a value which is always the 2nd (right) argument while a semicolon just ends statements. That allows the comma operator to be used inside other statements or to concatenate multiple statements to appear as one.
Here the function f(x) gets called and then x > y is evaluated for the if statement.
if( y = f(x), x > y ) An example when it's used just to avoid a the need for block
if( ... ) x = 2, y = 3; if( ... ) { x = 2; y = 3; } If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With
