ceil()

Returns the next whole number that is greater than or equal to the argument.

std::ceil(n);

Argument must be a double/float/long double, and the return value will be same type.

Use ceil() function to round up the double 12.3456:

#include <iostream>
#include <cmath>

int main() {
  double n = 12.3456;
  double result;

  result = std::ceil(n);

  std::cout << "The result is " << result << "!\n";
  // Output: The result is 13!
}