Error when using two variables in a for statement

Question

for (int a = 0, int x = 1; a < 2; a++, x++)
{
  // Body
}

When I do this, it shows me an error on that line at the part when I declare x.

The error is:

error: expected identifier or '('
        for (int a = 0, int x = 1; a < 2 && x < 3; a++, x++)

Please note that this was the first time I ever declared x.

This problem is related to cs50's filter.

I tried googling to see if the code itself was incorrect but all the example were like mine.

I tried replacing the , with ; but that just made another error saying it was expecting an expression at the very same place.

I also tried remove the int from x and declaring it at the start of the function but that also was an error saying it was shadowing a local variable.

Since they are both `int`s you can use: `for (int a = 0, x = 1; ...`. — wohlstad, Aug 04 '23 at 12:26
`int a = 0, int x = 1;` is not valid syntax. Take it out of the `for` loop and look at it and it'll probably become clear. — Ted Lyngmo, Aug 04 '23 at 12:27
Please show an example on the web where where you have found an example like yours. — Jabberwocky, Aug 04 '23 at 12:30
OT: why don't you get rid of `x` and use `(a + 1)` instead? And note that the error message wasn't from the code you gave: the end conditional is different. — Weather Vane, Aug 04 '23 at 12:35

score 4 · Answer 1 · answered Aug 04 '23 at 12:40

A for loop is a convenience construct around the more basic while loop to help programmers associate the variables being used and to constrain the scope of those used in the initializer clause. The initializer clause needs to be a valid initializer statment (or empty). Multiple definitions with type specifications separated by a comma is not a valid init statement.

int a = 0, int x = 1;

would need to be

int a = 0, x = 1;

And if variables with different types would be needed, you could use a while loop:

{ // scope limiter
    int a = 0;
    double x = 1.0;
    while(a < 2) {
        // Body
        ++a;
        ++x;
    }
}

... or a combination of the two:

{ // scope limiter
    double x = 1.0;
    for(int a = 0; a < 2; ++a, ++x) {
        // Body
    }
}

score 2 · Answer 2 · answered Aug 04 '23 at 12:30

2

Change to

for (int a = 0, x = 1; a < 2; a++, x++)

If you want multiple variables of different type, declare them before the loop.

answered Aug 04 '23 at 12:30

klutt

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Error when using two variables in a for statement

2 Answers2