...
struct Duomenys
{
...
int Balart[10]
...
};
...
void Suma(int suma[], int B[], int n, int k);
int main(){
...
A[i].Balart = Suma(A[i].Balart, A[i].art, n, k);
...
}
void Suma(int suma[], int B[], int n, int k)
...
error: incompatible types in assignment of 'void' to 'int[10]'
I assume you have the following line that you did not show:
Duomenys A;
Otherwise A would be undefined.
line 5: You're missing a ;
Line 13: Your subscripting is incorrect. Presumably, it is Balart that is subscripted, not A. However, since you didn't show the definition of A, that is only a guess. Where is A.art defined? Did you mean Balart?