Real-time based increment / decrement in C++ console - c++

Question

Is there a way to increment / decrement value of a varaible in correspondence to the real-time in a simple C++ console application without using third-party libraries.
For, e.g. in Unity3D game engine, there is something called Time.DeltaTime which gives the time it took to complete last frame. Now, I understand there are no draw update functions or frames in a console app, however what I'm trying to do is able to increment / decrement value of a variable such that, it changes with respect to the time something like,
variable = 0
variable = variable + Time.DeltaTime
so that the variable value increment each second. Is something like this possible in C++ 11 ? so, say if speed is 5 then after 5 seconds the variable has a value 5.
Bascially, I am creating a simple particle system where I want the particles to die after their MAX_AGE is reached. I am not sure how to implement that in a simple C++ console app.

Answer 1

For simple timing you can use std::chrono::system_clock. The tbb::tick_count is a better delta timer, but you said no third party libraries.

Answer 2

As you already know, delta time is the final time, minus the original time.
dt= t-t0
This delta time, though, is simply the amount of time that passes while the velocity is changing.
The derivative of a function represents an infinitesimal change in the function with respect to one of its variables. The derivative of a function with respect to the variable is defined as
f(x + h) - f(x)
f'(x) = lim -----------------
h->0 h
First you get a time, i.e NewTime = timeGetTime().
Then you subtract the old time from a new time you just got. call it delta time , dt.
OldTime = NewTime;
dt = (float) (NewTime - OldTime)/1000;
Now you sum dt into totaltime.
TotalTime += dt
So that when TotalTime reaches 5, you end the life of the particles.
if(TotalTime >= 5.0f){
//particles to die after their MAX_AGE is reached
TotalTime=0;
}
...
More interesting reading:
http://gafferongames.com/game-physics/
http://gafferongames.com/game-physics/integration-basics/
...
example code for Windows:
#include<time.h>
#include<stdlib.h>
#include<stdio.h>
#include<windows.h>
#pragma comment(lib,"winmm.lib")
void gotoxy(int x, int y);
void StepSimulation(float dt);
int main(){
int NewTime = 0;
int OldTime = 0;
int StartTime = 0;
int TimeToLive = 5000; //// TimeToLive 5 seconds
float dt = 0;
float TotalTime = 0;
int FrameCounter = 0;
int RENDER_FRAME_COUNT = 60;
// reset TimeToLive
StartTime = timeGetTime();
while(true){
NewTime = timeGetTime();
dt = (float) (NewTime - OldTime)/1000; //delta time
OldTime = NewTime;
// print to screen TimeToLive
gotoxy(1,1);
printf("NewTime - StartTime = %d ", NewTime - StartTime );
if ( (NewTime - StartTime ) >= TimeToLive){
// reset TimeToLive
StartTime = timeGetTime();
}
// The rest of the timestep and 60fps lock
if (dt > (0.016f)) dt = (0.016f); //delta time
if (dt < 0.001f) dt = 0.001f;
TotalTime += dt;
if(TotalTime >= 5.0f){
TotalTime=0;
StepSimulation(dt);
}
if(FrameCounter >= RENDER_FRAME_COUNT){
// draw stuff
//Render();
gotoxy(1,3);
printf("OldTime = %d \n",OldTime);
printf("NewTime = %d \n",NewTime);
printf("dt = %f \n",dt);
printf("TotalTime = %f \n",TotalTime);
printf("FrameCounter = %d fps\n",FrameCounter);
printf(" \n");
FrameCounter = 0;
}
else{
gotoxy(22,7);
printf("%d ",FrameCounter);
FrameCounter++;
}
}
return 0;
}
void gotoxy(int x, int y){
COORD coord;
coord.X = x; coord.Y = y;
SetConsoleCursorPosition(GetStdHandle(STD_OUTPUT_HANDLE), coord);
return;
}
void StepSimulation(float dt){
// calculate stuff
//vVelocity += Ae * dt;
}