Creating a calculator script

Question

I am trying to make a calculator with a bash script. The user enters a number, chooses whether they wish to add, subtract, multiply or divide. Then the user enters a second

Answer 1

The lesser-known shell builtin command select is handy for this kind of menu-driven program:

#!/bin/bash
while true; do
    read -p "what's the first number? " n1
    read -p "what's the second number? " n2
    PS3="what's the operation? "
    select ans in add subtract multiply divide; do
        case $ans in 
            add) op='+' ; break ;;
            subtract) op='-' ; break ;;
            multiply) op='*' ; break ;;
            divide) op='/' ; break ;;
            *) echo "invalid response" ;;
        esac
    done
    ans=$(echo "$n1 $op $n2" | bc -l)
    printf "%s %s %s = %s\n\n" "$n1" "$op" "$n2" "$ans"
done

Sample output

what's the first number? 5
what's the second number? 4
1) add
2) subtract
3) multiply
4) divide
what's the operation? /
invalid response
what's the operation? 4
5 / 4 = 1.25000000000000000000

---

If I was going to get fancy with bash v4 features and DRY:

#!/bin/bash

PS3="what's the operation? "
declare -A op=([add]='+' [subtract]='-' [multiply]='*' [divide]='/')

while true; do
    read -p "what's the first number? " n1
    read -p "what's the second number? " n2
    select ans in "${!op[@]}"; do
        for key in "${!op[@]}"; do
            [[ $REPLY == $key ]] && ans=$REPLY
            [[ $ans == $key ]] && break 2
        done
        echo "invalid response"
    done
    formula="$n1 ${op[$ans]} $n2"
    printf "%s = %s\n\n" "$formula" "$(bc -l <<< "$formula")"
done

Answer 2

How about this

calc ()
{
  (( d = $1 ))
  echo $d
}

output

$ calc '6 + 2'
8

$ calc '6 - 2'
4

$ calc '6 * 2'
12

$ calc '6 / 2'
3

Answer 3

#calculator

while (true) # while loop 1
do  
echo "enter first no"
read fno
if [ $fno -eq $fno 2>/dev/null ]; # if cond 1 -> checking integer or not
then
c=1
else
echo "please enter an integer"
c=0
fi # end of if 1
if [ $c -eq 1 ]; #if 2
then
break
fi # end of if 2
done # end of whie 1

while(true) #while loop 2
do
echo "enter second no"
read sno
if [ $sno -eq $sno >/dev/null 2>&1 ] # if cond 3 -> checking integer or not
then
c=1
else
echo "please enter an integer"
c=0
fi # end of if 3
if [ $c -eq 1 ] # if cond 4
then
break
fi # end of if 4
done #2

while(true) # while loop 3
do
printf "enter the operation (add,div,mul,sub) of $fno and $sno\n"
read op
count=0
##addition

if [ $op = add ] #if cond 5
then
echo "$fno+$sno is `expr $fno + $sno`"

#multiplication

elif [ $op = mul ]; 
then
echo "$fno*$sno is `expr $fno \* $sno`"

#substraction

elif [ $op = sub ] 
then
while(true) #while loop 3.1
do
printf "what do you want to do??? \n 1. $fno-$sno \n 2. $sno-$fno"
printf "\n press the option you want to perform?(1 or 2)\n"
read opt
if [ $opt = 1 ] #if cond 5.1
then
echo "$fno-$sno is `expr $fno - $sno`"
break
elif [ $opt = 2 ] 
then
echo " $sno-$fno  is `expr $sno - $fno`"
break
else "please enter valid options to proceed(1 or 2)";
clear
fi #end of if 5.1
done  # end of 3.1

#division
elif [ $op = div ]
then
while(true) # whilw loop 3.2
do
printf "what do you want to do??? \n 1. $fno/$sno \n 2. $sno/$fno"
printf "\n press the option you want to perform?(1 or 2)\n"
read opt
if [ $opt = 1 ] #if cond 5.2
then
echo "$fno divided by $sno is  `expr $fno / $sno`"
break
elif [ $opt = 2 ]
then
echo " $sno divided by $fno  is `expr $sno / $fno`"
break
else 
clear
fi #end of if 5.2
done  # end of 3.2
else 
echo "valid option please!!!"
count=1
fi # end of if 5

if [ $count -eq 0 ] #if cond 6
then
echo "Do you want to do more ops"
echo "(y/n)"
read ans
clear
if [ $ans = n ] # if 6.1
then
break
fi # end of if 6.1
fi #end of if 6
done  #end of while 3

Answer 4

!/bin/bash

PS3="what's the operation? " declare -A op=([add]='+' [subtract]='-' [multiply]='*' [divide]='/')

while true; do read -p "what's the first number? " n1 read -p "what's the second number? " n2 select ans in "${!op[@]}"; do for key in "${!op[@]}"; do [[ $REPLY == $key ]] && ans=$REPLY [[ $ans == $key ]] && break 2 done echo "invalid response" done formula="$n1 ${op[$ans]} $n2" printf "%s = %s\n\n" "$formula" "$(bc -l <<< "$formula")" done

Answer 5

Please use the following script.

clear
sum=0
i="y"

echo " Enter one no."
read n1
echo "Enter second no."
read n2
while [ $i = "y" ]
do
echo "1.Addition"
echo "2.Subtraction"
echo "3.Multiplication"
echo "4.Division"
echo "Enter your choice"
read ch
case $ch in
    1)sum=`expr $n1 + $n2`
     echo "Sum ="$sum;;
        2)sum=`expr $n1 - $n2`
     echo "Sub = "$sum;;
    3)sum=`expr $n1 \* $n2`
     echo "Mul = "$sum;;
    4)sum=`expr $n1 / $n2`
     echo "Div = "$sum;;
    *)echo "Invalid choice";;
esac
echo "Do u want to continue ?"
read i
if [ $i != "y" ]
then
    exit
fi
done

Answer 6

Wrapping Code in a Loop

If you just want to wrap your code in a Bash looping construct, and are willing to hit CTRL-C to terminate the loop rather than do something more fancy, then you can wrap your code in a while-loop. For example:

while true; do
    : # Your code goes here, inside the loop.
done

Just make sure to move your unconditional exit statement out of the body of the loop. Otherwise, the loop will terminate whenever it reaches that line.