I am implementin a utility to provide the process statistics by reading the /proc/<pid>/stat.
However , I am not able to figure out how to calculate the number of Voluntary context switches and involulentary context switches.
I am using RHEL 5.8

Try /proc/<pid>/status instead:

The kernel version that we have is 2.6.18-164.el5. On this we do not have VCTX,ICTX and SYSC available in /proc/<pid>/status
Pasted below is an extract for you.
Name: java
State: S (sleeping)
SleepAVG: 0%
Tgid: 2067
Pid: 2067
PPid: 1
TracerPid: 0
Uid: 11310 11310 11310 11310
Gid: 2003 2003 2003 2003
FDSize: 512
Groups: 2003 2004
VmPeak: 2136508 kB
VmSize: 465064 kB
VmLck: 0 kB
VmHWM: 161160 kB
VmRSS: 161156 kB
VmData: 412060 kB
VmStk: 132 kB
VmExe: 36 kB
VmLib: 23452 kB
VmPTE: 692 kB
StaBrk: 48f5f000 kB
Brk: 48fee000 kB
StaStk: 7fff0d6097e0 kB
Threads: 163
SigQ: 0/529408
SigPnd: 0000000000000000
ShdPnd: 0000000000000000
SigBlk: 0000000000000000
SigIgn: 0000000000000003
SigCgt: 1000000189005ccc
CapInh: 0000000000000000
CapPrm: 0000000000000000
CapEff: 0000000000000000
Cpus_allowed: 00000000,00000000,00000000,00000000,00000000,00000000,0000ffff,ffffffff
Mems_allowed: 00000000,0000000f

It doesn't look like that information was available under /proc until 2.6.23, you may be out of luck...