Find nCr.

 Program

echo -e  "Enter n: \c"

read n

echo -e "Enter r: \c"

read r

i=2

nf=1

temp=`expr $n - $r`

tf=1

rf=1

ncr=1

while test $i -le $n

do

   nf=`expr $nf\*$i`

   i=`expr $i + 1`

done

nf=`echo "$nf" | bc`

i=2

while test $i -le $temp

do

  tf=`expr $tf\*$i`

  i=`expr $i + 1`

done

tf=`echo "$tf" | bc`

i=2

while test $i -le $r

do

  rf=`expr $rf\*$i`

  i=`expr $i + 1`

done

rf=`echo "$rf" | bc`

temp2=`echo "$nf / $tf" | bc`

ncr=`echo "$temp2 / $rf" | bc`

echo "nCr = $ncr"

Output

sh ncr.sh

Enter n: 5

Enter r: 4

nCr = 5

sh ncr.sh

Enter n: 9

Enter r: 4

nCr = 126

sh ncr.sh

Enter n: 12

Enter r: 5

nCr = 792