error: expected initializer before 'int'

Question

i am trying to pass 2D array as parameter in function, on building I got error written in title

and error message pointed this line and pointed before int corresponding to size ......

=> bool dia_sum(int arr[][int size]) {
vector<int> sum{};
int add{};
...................
...............
return false
}

I am not able to resolve it actually can't understand what is it?

Answer 1

Noob In C++ multidimensional arrays have to have fixed sizes for all dimensions but the first. You declared your function with int arr[][int size] which is not possible because these dimensions have to be known at compile time. So for example int arr[][5] would work.

When you want to work with dynamic sized multidimensional arrays in C++ there are several ways to do this. For example you can just allocate a dynamic array like this: int* arr = new int[size*size]; and access elements like this: arr[x+y*size] this way you can pass the pointer to a function. Of course don't forget to delete[] arr; after you don't need it anymore.

There are also other ways of doing this like using std::vector

Answer 2

The problem is literally what the compiler is saying
"left operand of the comma operator has no effect"

That is, the left side of the expression on line 104
"i >= 0, j < size2"
^^^^^^
has no effect, or in other words, is useless. This is because the comma operator ignores its left operand. See this:
https://en.m.wikipedia.org/wiki/Comma_operator

To fix it, use the logical AND operator (&&) instead of the comma
"i >= 0 && j < size2"

You need to do the same thing for line 109.

Also, on line 37, you are making the same mistake you were making in your previous code
`int matrix[size][size]`

A non-const integer variable cannot be used to declare the size of the array as the size must be known to the compiler at compile time. You need to either use a integer literal (like "int matrix[2][2]") or a const variable. It works on GCC, but it doesn't work on most other compilers.

Again you need to allocate a block of memory
`int *matrix = new int[size][size];`

Answer 3

Noob
sorry, I didn't read your "2nd query".

The error is because it is invalid syntax. Just like the line
`int i{0}, int j{1}`
is invalid syntax, the line
`for (int i{0}, int j{0};....)`
is also invalid syntax.

You only need to specify the type at the start of the declaration, like so
`for(int i{0}, j{0};...)`

Answer 4

can i see ur array and how you pass it?

Answer 5

code link:
https://code.sololearn.com/c9817a1A205a

Answer 6

@Hape thanks bro,
I have modified my code ,working fine but still giving warning message

warning: left operand of comma operator has no effect [-Wunused-value]
in line...........
for(i = size1-1,j=0; i>=0, j< size2 ; i--,j++) ...............
but I couldn't figure out how comma operator is unused here?

Also 2nd query is(not related to above , just a doubt)....
if I do
for(int i{0} ; i < 5 ; i++) //fine
if I do
for(int i{0} , int j{0}; i < 5 , j < 5; i++, j++) //gives error
error says ,I) expected expression before int,
II) can't do list initialization

please tell me why ? and what is the reasons?