Digital calculation

No1=1

No2=2

1、 let result=No1+No2   let No1++    let No1+=3

2、 result=$[No1+No2]

3、 result=$((No1+No2))

4、 result=`expr $No1 + $No2`   # '$' and space are necessary.

5、 echo "$No1+No2"|bc

echo "scale=3; 3/4"|bc      #keep three decimal places

echo "obase=2; ibase=10; 100"|bc     #Convert decimal to binary.

echo "sqrt(100)"|bc

echo "10^5"|bc