Changes

for (int i=0; i <= nx-1; i++)

{

if (i*dx >= 0.5 && i*dx <= 1)

u[i][it] = un[i][it-1] - c*dt/dx*(un[i][it-1]-un[i-1][it-1]);

}

}'''

'''

for (int k = 0; k <= nx - 1; k++)

u[m * nx + it] = un[m * nx + it - 1] - c*dt / dx*(un[m * nx + it - 1] - un[(m - 1) * nx + it - 1]);

}'''