Is the code for the trapezoid method written correctly in C++?

Question

Programming

h = (b - a) / n;
  for (int i = 1; i <= (n - 1); i++)
    S += f(a + h*i);
  integ = h * ((f(a) + f(b)) / 2 + S);

Answer 1

At least describe what f() means for you. And so some kind of stub of code, which still needs to be thought out on its own.
An example from the cyberforum.

#include <cmath>
#include <cstdio>
#include <cstdlib>
 
typedef double(*function)(double);
 
double integral(function f, double a, double b, unsigned step_count) {
  double sum = .0, step;
  size_t i;
  if (0 == step_count) return sum;
 
  step = (b - a) / (1.0 * step_count);
  for ( i = 1 ; i < step_count ; ++i ) {
    sum += f (a + i * step);
  }
  sum += (f(a) + f(b)) / 2;
  sum *= step; 
  return sum;
}
 
double f (double x) {
  return 2 * x;
}
 
int main() {
  printf ("\\int_0^10(x) = %f\n", integral(f, 0, 10, 15));
}

Answer 2

Answering the question: Yes, this piece of code is correct .
Recommendations for the future:
1) When asking a question, it is advisable to write in a little more detail.
2) To check the code, you can make a formula that it implements and compare with the theoretical one.