#include <math.h>
#include <stdlib.h>
#define K 100
#define pi 3.141592653589793
double pho[K+1], phn[K+1]; double t = 0, dt = 1.;
void print(){int j; for(j=0; j<K; ++j)
  {if(!(j%10)) printf("\n%4d ", j); printf("%8.5f ", pho[j]);}
  printf("\n");};

int main(){

{// Initial boundary conditions:
int j=K+1; while(j--) pho[j] = sin(2*pi*3*j/100);}
{//Explicit calculation:
  print(); {t += dt;
  {int j; for(j=1; j<K; ++j) {
    double flowrate = (pho[j-1]-pho[j]) + (pho[j+1]-pho[j]);
    phn[j] = pho[j] + flowrate*dt;}}
  {// Copy phn to pho:
    int j=K+1; while(j--) pho[j] = phn[j];}
 }
 print();}}