sine wave generation in c++

Question

I am trying to generate a set of points, which when plotted as a graph represent a sine wave of 1 cycle. The requirements are :

• a sine wave of 1 cycle
  
• lower limit = 29491
  
• upper limit = 36043
  
• no of points = 100
  
• Amplitude = 3276
• zero offset = 32767

Code :

int main()
{
    ofstream outfile;
    outfile.open("data.dat",ios::trunc | ios::out);
    for(int i=0;i<100;i++)
    {
        outfile << int(3276*sin(i)+32767) << "\n";
    }
    outfile.close();
    return 0;
}

I am generating and storing the points in a file. When these points are plotted I get the following graph.

But I only need one cycle. How can I do this?

Solution 1

taking into the formula of sine wave:

y(t) = A * sin(2 * PI * f * t + shift)

where:

A = the amplitude, the peak deviation of the function from zero.
f = the ordinary frequency, the number of oscillations (cycles)
t = time
shift = phase shift

would be:

y[t] = AMPLITUDE * sin (2 * M_PI * 0.15 * t + 0) + ZERO_OFFSET;
                                   ^^^ f = 15 cycles / NUM_POINTS = 0.15 Hz

To have one full-cycle, loop from y[0:t) where t is the time or number of points it takes to have a full cycle (i.e. wavelength)

Solution 2

It appears you need 100 samples for one cycle, so you probably need this:

...
#define _USE_MATH_DEFINES
#include <math.h>
...
#define NB_OF_SAMPLES 100
...
  double angle = 0.0;
  for (int i = 0; i < NB_OF_SAMPLES; i++)
  {
    outfile << int(3276 * sin(angle) + 32767) << "\n";
    angle += (2 * M_PI) / NB_OF_SAMPLES;
  }
...

Or better:

#define NB_OF_SAMPLES 100
#define OFFSET        3276
#define AMPLITUDE     32767

...
  double angle = 0.0;
  for (int i = 0; i < NB_OF_SAMPLES; i++)
  {
    outfile << int(AMPLITUDE * sin(angle) + OFFSET) << "\n";
    angle += (2 * M_PI) / NB_OF_SAMPLES;
  }
...

Solution 3

A full cycle consists of 360 degrees. samples needed is 100.
So step size is 3.6

int main()
{
    ofstream outfile;
    outfile.open("data.dat",ios::trunc | ios::out);
    for(int i=0;i<101;i++)
    {
        float rads = M_PI/180;
        outfile << (float)(3276*sin(3.6*i*rads)+32767) << endl;
    }
    outfile.close();
    return 0;
}

If number of samples is 200, then step size if 360/200 = 1.8

int main()
{
    ofstream outfile;
    outfile.open("data.dat",ios::trunc | ios::out);
    for(int i=0;i<201;i++)
    {
        float rads = M_PI/180;
        outfile << (float)(3276*sin(1.8*i*rads)+32767) << endl;
    }
    outfile.close();
    return 0;
}

Output:

Comments

[underscore_d]

/i er, no. You mean * (i / 100.0). I mean, the 1st iteration of what you wrote is instant UB!

[Some programmer dude]

Please note that M_PI is not a standard macro, not all libraries define it.

[Paul Floyd]

@Some programmer dude Have you ever used a compiler/library that didn't have it easily available?

[Some programmer dude]

I have seen it missing somewhere, but it was some time ago. However, considering that it's included with the MSVC headers and mandated by POSIX it's almost (but not quite) universal.