How can I invoke both BASH and CSH shells in a same script

Question

In the same script, I want to use some CSH commands and some BASH commands. Invoking one after the other giving me problems despite I am following the different syntax for respective shells. I want to know where is mistake in my code Your suggestions are appreciated!!

I am a beginner to shell, especially so for CSH. but the code I got has been written in CSH entirely. Since I have some familiarity with CSH, I wanted to tweak the existing CSH code by including BASH commands, which I am comfortable using it. When I tried BASH commands after CSH by invoking !#/bin/bash, it is giving some errors. I want to know if I am missing any options!!

#!/bin/csh
----
----
----
#!/bin/bash
dir2in="/nethome/achandra/NCEI/CCSM4_Historical/Forecasts"
filin2 ="ccsm4_0_cfsrr_Fcst.${ENS}.cam2.h1.${yyear[${iimonth}]}-${mmon[${iimonth}]}-${ssday}-00000.nc"
cp $dirin/$filin /nethome/achandra/NCEI/CCSM4_Historical_Forecasts/
ln -s /nethome/achandra/NCEI/CCSM4_Historical/Forecasts/$filin /nethome/achandra/NCEI/CCSM4_Historical_Forecasts/"${$filin%.nc.cdo}.nc"
#!/bin/csh 

I am getting errors such as "dirin: Undefined variable."