// https://godbolt.org/z/dKPo7andE
#include <iostream>
#include <iomanip> // setprecision, fixed
constexpr int framesPerSec = 25;
constexpr int runtimeInSecs = 3600;
constexpr int framesTotal = runtimeInSecs * framesPerSec;
constexpr float frametime = 1.0f / framesPerSec;
int main() {
float filmtime = 0.f;
for(int n=1; n <= framesTotal; ++n) { // 1 .. framesTotal, because of formula
filmtime = frametime * n; // scale
// ... here code for this frame ...
}
std::cout << std::setprecision(10) << std::fixed
<< filmtime << '\n'; // output: 3600.0000000000
}