  In this work, we observe that in the presence of the string cloud parameter
$a$ and the quintessence parameter $\gamma$, with the equation of state
parameter $\omega_q={-2}/{3}$ the radius of the shadow of the Schwarzschild
black hole increases as compared with the pure Schwarzschild black hole case.
The existence of both quintessential dark energy and cloud of strings magnify
the shadow size and hence the strength of the gravitational field around the
Schwarzschild black hole increases. Using the data collected by the Event
Horizon Telescope (EHT) collaboration for the M87* and Sgr A*, we obtain upper
bounds on the values of the parameters $a$ and $\gamma$. Further, we see the
effects of the parameters $a$ and $\gamma$ on the rate of emission energy for
the Schwarzschild black hole. We notice that the rate of emission energy is
higher in the presence of clouds of string and quintessence. Moreover, we study
the weak deflection angle using the Gauss-Bonnet theorem. We show the influence
of the cloud of string parameter $a$ and the quintessential parameter $\gamma$
on the weak deflection angle. We notice that both the parameters $a$ and
$\gamma$ increase the deflection angle $\alpha$.
