How to properly declare variables and set an array?

Question

C++ / C#

Hello everyone, please help, how in this code, code snippet, to correctly declare variables and set an array?
The program is designed to solve such an equation:

I don’t understand how to correctly declare variables in this code, I know that int cannot be divided by int, and there are problems with creating an array VS constantly swears that "N is an undeclared identifier
" knowledge is still weak.
Thanks in advance for any help in this matter)
Here is the code itself

double f[N];
double h;
double res = 0;
h = (b-a)/n;
for(int i = 1; i<N + 1; i++)
{
f[i-1] = (a + (i - (1/2)*h)) / (1 + (a+(i - 1/2 ) * h));
}
 
for(int i = 0; i<N; i++)
res+=f[i];
 
res*=h;

Answer 1

First, the variable N is not defined anywhere, just like a, b and n.
Secondly, you don't need an array, just add the resulting f _i at once .
Thirdly, you can divide int by int, but the result will also be of type int.
Fourth, since you are working in real numbers, then write not 1/2, but 0.5, 1/2. or 1./2 to make the compiler understand that these subexpressions should be treated as real.