Plots not showing up

My plots are currently not showing up. Also, I was wondering if there's a way for me to put figures 1 & 2 in one graph. Thank you for the help! I've attached my code below.

alt=0
Ma=0.92
deltaH=18100
pa=14.69
mdot=100
Tt4=2450
Ta=518.7
gamma=1.4
R=0.2399565

%Diffuser
aa=sqrt(gamma*R*32.17*Ta);
ua=Ma*aa;
Tta_Ta=(1+0.5*(gamma-1).*Ma^2);
Tta=506.21 * 1.03872;
Tt2=Tta;
Pta_Pa=(Tta_Ta)^((gamma)/(gamma-1));
Pt2_Pa=Pta_Pa;
Pt2=Pta_Pa*pa;
pi_c=linspace(5,20);
%Compressor
P_t3=pi_c.*P_t2;
tau_c=pi_c.^((gamma-1)./gamma);
T_t3=tau_c*T_t2;
%Primary Combustor
P_t4=P_t3;
m_dotf=(m_dot*Cp*(T_t4-T_t3))./ deltaH;
%Turbine
T_t5=1707.751
tau_t=T_t5./T_t4;
pi_t=0.2827511
P_t5=pi_t.*P_t4;
T_t55=T_t5;
P_t55=pt_5;
%Primary Nozzle
T_t6=T_t55;
P_t6=P_t55;
T_8=T_t6.*((P_8./P_t6).^((gamma-1)/gamma));
u_8=[2*Cp.*(T_t6-T_8)*32.17*778.16].^0.5;
a_8=(gamma*R*T_8.*32.17).^0.5;
M_8=u_8./a_8;
A_8=m_dotf.*144./(rho_8.*u_8*32.17);
%Total Thrust and TSFC
F=mdot.*u_8-mdot.*u_a;
nDF=(F.*32.17)./(mdot.*a_a);
TSFC=mdot./F; 

TSFCaa=TSFC.*aa;

%% Graphs
%1. 
f1=figure(1);clf;
plot (pi_c,TSFCaa,'k')
title('Figure 1. TSFC_a vs. \pi_c');
xlabel('\pi_c')
ylabel('TSFC_a_a')

f2=figure(2);clf;
plot(pi_c,nDF,'k')
title ('Figure 2. nDF_a vs. \pi_c');
xlabel('\pi_c')
ylabel('nDF_a')

[KSSV]

In the given code all the variables are not defined. Give us all the variables.

You can show up two graphs in one using hold on. Read about it.