/* Compute sine waves program */

#include<stdio.h>
#include<math.h>
#define pi 3.14159265305

int imax;
float frequency;

void readinvalues(int *imax,float *frequency)
{
  /*This subroutine inputs the user for the  */
  /*the number of values of the sine wave to compute*/
  /*and the frequency of the sine wave */
  int ivalue;
  float freqvalue;
  printf("How many values of the sine wave do you wish to compute?\n");
  scanf("%i",&ivalue);
  printf("OK -- running for %i values.\n",ivalue);
  printf("What is the frequency of the sine wave?\n");
  scanf("%f",&freqvalue);
  printf("OK -- running for frequency %f.\n",freqvalue);
  *imax=ivalue;
  *frequency=freqvalue;
  /*When we are changing the variables within a subroutine in C*/
  /*we need to use pointers, rather than just the variable name*/
  return;
}


void printoutsines(int imax,float frequency)
{
  /*This subroutine prints out the value of */
  /*the sine wave for the different values of time, or */
  /*whatever the x-axis is*/
  int i;
  float x,y;
  FILE *fp;
  printf("Running for %i and frequency %f",imax,frequency);
  fp = fopen ("out_sines", "w");
  for (i = 0;i < imax; i=i+1 ) {
    x = float(i)*frequency*2.0*pi/100.0;
    y =sin(x);
    fprintf(fp,"%f %f \n",x/(2.0*pi),y);	 
  }
  /* By dividing by 2*pi in the previous line, we get the x-variable*/
  /* to be in units of periods, rather than radians*/
  return ;
} 

main()
{
  int i,imax;
  float frequency;
  readinvalues(&imax,&frequency);
  printoutsines(imax,frequency);
}