Nested if statements with nested loops - linux

Question

I am trying to make a simple calculator. I am sure if you even just glanced at this code you will see what I am trying to do.
Enter a number, then choose an operand, then vim should print out a table up to 15 with your number and operand...
Maybe this method is silly, trying to nest a load of loops in nested if statements. But I am new to bash.
The error is 'Unexpected token near else' line 24 but I feel there is a fundamental issue with the nests I do not understand.
Here is current code.
#!/bin/bash
choice=6
read -p "Enter a number bruv" num
#choose operand.
echo "Now choose an operand comrade"
#choices
echo "1. *"
echo "2. +"
echo "3. -"
echo "4. /"
echo "5. ^"
echo -n "Please choose [1,2,3,4,5]"
while [ $choice -eq 6 ]; do
read choice
if [ $choice -eq 1 ] ; then
for((i=0;i<=15;i++))
do
echo -n "$i * $num = $[ $i * $num ] "
echo " "
else
if [ $choice -eq 2 ] ; then
for((i=0;i<=15;i++))
do
echo -n "$i + $num = $[ $i + $num ] "
echo " "
else
if [ $choice -eq 3 ] ; then
for((i=0;i<=15;i++))
do
echo -n "$i - $num = $[ $i - $num ] "
echo " "
else
if [ $choice -eq 4 ] ; then
for((i=0;i<=15;i++))
do
echo -n "$i / $num = $[ $i / $num ] "
echo " "
else
if [ $choice -eq 5 ] ; then
for((i=0;i<=15;i++))
do
echo -n "$i ^$num = $[ $i ^$num ] "
echo " "
else echo "Please choose between 1 and 5!!!"
echo "1. *"
echo "2. +"
echo "3. -"
echo "4. /"
echo "5. ^"
echo -n "Please choose [1,2,3,4,5]"
fi
fi
fi
fi
fi
done
Would it be better to implement this?
# !/bin/bash
# Take user Input
echo "Enter number : "
read a
# Input type of operation
echo "Enter Choice :"
echo "1. Addition"
echo "2. Subtraction"
echo "3. Multiplication"
echo "4. Division"
echo "5. Power"
read ch
# Switch Case to perform
# calulator operations
case $ch in
1)res=`for((i=0;i<=15;i++))
do
echo -n "$i - $num = $[ $i - $num ] "
echo " "`
;;
2)res=`for((i=0;i<=15;i++))
do
echo -n "$i - $num = $[ $i - $num ] "
echo " "`
;;
3)res=`for((i=0;i<=15;i++))
do
echo -n "$i - $num = $[ $i - $num ] "
echo " "`
;;
4)res=`for((i=0;i<=15;i++))
do
echo -n "$i - $num = $[ $i - $num ] "
echo " "c`
;;
esac
echo "Result : $res" ```

Answer 1

Here is a solution, using a function:
#! /bin/bash
ITER_MAX=15
show_values() # n op
{
local n=$1 op=$2
for ((i=0; i<=ITER_MAX; i++)); do
((i>0)) && echo -n " ; "
echo -n "$i $op $n = $((i $op n))"
done
echo
}
# Take user Input
read -p "Enter number : " a
# Input type of operation
echo "Enter Choice (Ctrl+C to stop):"
PS3=">> "
select ch in Addition Subtraction Multiplication Division Power ; do
case "$ch" in
Add*) op="+" ;;
Sub*) op="-" ;;
Mul*) op="*" ;;
Div*) op="/" ;;
Pow*) op="**" ;;
*) echo "Bad choice, abort" >&2 ; break ;;
esac
show_values "$a" "$op"
done
Some explanations:
(( )) is arithmetic evaluation and $(( )) is arithmetic expansion
((i>0)) && echo -n " ; " is equivalent to if ((i>0)); then echo -n " ; " ; fi
read -p "Enter number : " a is equivalent to echo -n "Enter number : " ; read a
about select, see help select in your bash terminal.

Answer 2

Use https://www.shellcheck.net/
Line 20:
for((i=0;i<=15;i++))
^-- SC1009: The mentioned syntax error was in this for loop.
^-- SC1073: Couldn't parse this arithmetic for condition. Fix to allow more checks.
Line 21:
do
^-- SC1061: Couldn't find 'done' for this 'do'.
Line 24:
else
^-- SC1062: Expected 'done' matching previously mentioned 'do'.
^-- SC1072: Unexpected keyword/token. Fix any mentioned problems and try again.
An alternate take:
read -p "Enter a number and an operator: " -a a
for n in {1..15}; do printf "%+10s\n" $((${a[#]} $n)); done
-p tells read to supply a prompt. -a reads into an array (named a here).
{1..15} is built-in bash sequence syntax.
%+10s tells printf to space-pad/right justify out to 10 characters.
${a[#]} is replaced with all the elements of the array - the number and then operator.
$(( ... )) does arithmetic processing and replaces itself with the result (as a string).
So if you enter "10 *" then $((${a[#]} $n)) processes 10 * 1 the first time, so printf "%+10s\n" $((${a[#]} $n)) outputs " 10" with a trailing newline character. Then the loop replaces the 1 with the next number on each iteration, up to 15. This also allows other operators, such as % for modulus, but will crash if something invalid is given.
If you want error checking -
while [[ ! "${a[*]}" =~ ^[0-9][0-9]*\ ([*/+-]|\*\*)$ ]]
do read -p "Enter a, integer and an operator (one of: + - * / **) " -a a
done
for n in {1..15}; do printf "%+10s\n" $((${a[#]} $n)); done
If you want floating point math, try bc:
while [[ ! "${a[*]}" =~ ^[0-9]+.?[0-9]*\ ([*/+-]|\*\*)$ ]]
do read -p "Enter a, integer and an operator (one of: + - * / **) " -a a
done
for n in {1..15}; do printf "%+15s\n" $(bc -l <<< "scale=3;${a[#]} $n"); done
Personally, I'd put the inputs on the command line. Less futzy, though it might require quoting the * operator, depending on how you run it and what's in the directory.
#!/bin/bash
me=${0##*/}
use="
use: $me {number} {operator} [iterations] [scale]
Numbers may include one decimal point.
Operators must be one of: + - * / **
"
while getopts "n:o:i:s:" arg
do case $arg in
n) n="$OPTARG" ;;
o) o="$OPTARG" ;;
i) i="$OPTARG" ;;
s) s="$OPTARG" ;;
*) printf "%s\n" "Invalid argument '$arg' $use";
exit 1;;
esac
done
[[ -n "$n" && -n "$o" ]] || { echo "$use"; exit 1; }
[[ "$n" =~ ^[0-9]+.?[0-9]*$ ]] || { printf "%s\n" "Invalid number '$n' $use"; exit 1; }
[[ "$o" =~ ^([*/^+-]|\*\*)$ ]] || { printf "%s\n" "Invalid operator '$o' $use"; exit 1; }
[[ "${i:=15}" =~ ^[0-9]+.?[0-9.]$ ]] || { printf "%s\n" "Invalid number '$i' $use"; exit 1; }
[[ "${s:=3}" =~ ^[0-9]+$ ]] || { printf "%s\n" "Invalid scale '$s' (must be an integer) $use"; exit 1; }
c=1
while ((c < i))
do printf "%+15s\n" $(bc -l <<< "scale=$s; $n $o $c")
((c++))
done