g = 9.8;
l = 1;
theta[1] = Pi/4;
omega[1] = 0;
time[1] = 0;
deltatime = 0.01;
thetavstime = {{time[1], theta[1]}};
omegavstime  =  {{time[1], omega[1]}};
For[j = 0; 
      j < 180, 
theta[1] = 
        j*Pi/180;
For[i = 1, 
          i < 400, 
omega[i + 1] = 
            omega[i] - g/l*Sin[theta[i]]*deltatime; 
theta[
              i + 1] = 
            theta[i] + omega[i + 1]*deltatime; 
time[
              i + 1] = time[i] + deltatime; 
thetavstime = 
            Append[thetavstime, {time[i + 1], 
                theta[i + 1]}]; 
omegavstime = 
            Append[omegavstime, {time[i + 1], 
                omega[i + 
                    1]}]; 
i++;]
ListPlot[thetavstime];
ListPlot[
        omegavstime];