calculate determinant of matrix with thread - multithreading

Question

ı want to calculate determinant of matrix with thread but i have a error "term does not eveluate to a function taking 0 arguments" ı want to solve big matrix with thread and parsing matrix,what can ı do
int determinant(int f[1000][1000], int x)
{
int pr, c[1000], d = 0, b[1000][1000], j, p, q, t;
if (x == 2)
{
d = 0;
d = (f[1][1] * f[2][2]) - (f[1][2] * f[2][1]);
return(d);
}
else
{
for (j = 1; j <= x; j++)
{
int r = 1, s = 1;
for (p = 1; p <= x; p++)
{
for (q = 1; q <= x; q++)
{
if (p != 1 && q != j)
{
b[r][s] = f[p][q];
s++;
if (s > x - 1)
{
r++;
s = 1;
}
}
}
}
for (t = 1, pr = 1; t <= (1 + j); t++)
pr = (-1)*pr;
c[j] = pr*determinant(b, x - 1);
}
for (j = 1, d = 0; j <= x; j++)
{
d = d + (f[1][j] * c[j]);
}
return(d);
}
}
int main()
{
srand(time_t(NULL));
int i, j;
printf("\n\nEnter order of matrix : ");
scanf_s("%d", &m);
printf("\nEnter the elements of matrix\n");
for (i = 1; i <= m; i++)
{
for (j = 1; j <= m; j++)
{
a[i][j] = rand() % 10;
}
}
thread t(determinant(a, m));
t.join();
printf("\n Determinant of Matrix A is %d .", determinant(a, m));
}

Answer 1

The immediate problem is that here: thread t(determinant(a, m)); you pass the result of calling determinant(a, m) as the function to execute, and zero arguments to call that function with - but an int is not a function or other callable object, which is what the error you got complains about.
std::thread's constructor takes the function to run and the arguments to supply separately, so you would need to call std::thread(determinant, a, m).
Now we have another problem, std::thread doesn't provide a way to retrieve the return value, and so you calculate it again here: printf("\n Determinant of Matrix A is %d .", determinant(a, m));.
To fix this, we can use std::async from the <future> header, which will manage the thread handling for us, and lets us retrieve the result later:
auto result = std::async(std::launch::async, determinant, a, m);
int det = result.get()
This will run determinant(a,m) on a new thread, and return a std::future<int> into which the return value may eventually be placed.
We can then try to retrieve that value with std::future::get(), which will block until the value can be retrieved (or until an exception occurs in the thread).
In this example, we still execute determinant in a pretty serial fashion, since we delegate the work to a thread, then wait for that thread to finish its work before continuing.
However we are now free to store the future, and defer calling std::future::get() until we actually need the value, potentially much later in your program.
There are a few other problems in the rest of your code:
all your array indexing is off by one (array indices run from 0 to N-1 in C and C++)
a few of the variables you're using don't exist (like a and m)
C-arrays are passed by pointer, so if you ever change the code not to block on the thread right there, the array will go out of scope and your thread may read garbage from the dangling pointer. If you use a proper container like std::array or std::vector, you can pass it by value so your thread will own the data to operate on for its entire lifetime.