#!/usr/local/bin/dash
#
#!/bin/bash
#
# 'calc' - A basic calculator for average sized numbers.
#
# OSX 10.13.6, default bash terminal.
# Another exercise in futility by B.Walker.
# Public Domain.
# Accurate enough to nine decimal places.
# USAGE: calc NUMBER1 +|-|*|/ NUMBER2
#
# In 64 bit mode.
# Total upper limit = +9223372036.85477; 64 bit signed integer = 9223372036854775807.
# Total lower limit = -9223372036.85477; 64 bit signed integer = 9223372036854775808.
# This allows nine places for the decimal component.

# Numerical variables.
NUM1="$1"
NUM2="$3"
# Equalise the decimal places.
FP1=$( printf "%.9f" "$NUM1" )
FP2=$( printf "%.9f" "$NUM2" )

# Calculation mode variable, limited error correction.
CALC="$2"
if [ "$NUM1" = "" ] || [ "$NUM2" = "" ] || [ "$CALC" = "" ]
then
	echo "USAGE: calc NUMBER1 +|-|*|/ NUMBER2"
	exit 1
fi

# Remove the decimal point(s).
INT1="${FP1%.*}${FP1#*.}"
INT2="${FP2%.*}${FP2#*.}"
# Remove all leading zeros.
INT1=$( printf "%.f" "$INT1" )
INT2=$( printf "%.f" "$INT2" )

# Addition and subtraction.
if [ "$CALC" = "+" ] || [ "$CALC" = "-" ]
then
	if [ "$CALC" = "+" ]
	then
		SUM=$(( (INT1)+(INT2) ))
	fi
	if [ "$CALC" = "-" ]
	then
		SUM=$(( (INT1)-(INT2) ))
	fi
	# Internal Variables.
	LENGTH="${#SUM}"
	MINUS="$SUM"
	FLOAT=""
	COUNT="0"

	# Detect the minus sign, save and delete.
	while [ "$COUNT" -le "$LENGTH" ]
	do
		MINUS="${MINUS%?}"
		if [ "$MINUS" = "-" ]
		then
			SUM="${SUM#?}"
			MINUS="-"
			break
		fi
		COUNT=$(( COUNT+1 ))
	done

	# Give a positive sign on the final result if it is not negative.
	# This condition can be removed if required.
	if [ "$MINUS" = "" ]
	then
		MINUS="+"
	fi

	# Pad a float result of less that 1.0 with leading zeros if required.
	LENGTH=${#SUM}
	if [ "$LENGTH" -le "9" ]
	then
		FLOAT=$( printf "%09d" "$SUM" )
		SUM="$FLOAT"
	fi

	# Obtain the integer part.
	INT="${SUM%?????????}"
	if [ "$INT" = "" ]
	then
		INT="0"
	fi

	# Obtain the float part.
	if [ "$LENGTH" -ge "10" ]
	then
		COUNT="10"
		GETFLOAT=""
		while [ "$COUNT" -le "$LENGTH" ]
		do
			GETFLOAT="$GETFLOAT"'?'
			COUNT=$(( COUNT+1 ))
		done
		FLOAT="${SUM#${GETFLOAT}}"
	fi
	RESULT="${INT}.${FLOAT}"
	printf "%s%.9f\n" "$MINUS" "$RESULT"
fi

# Multiplication.
if [ "$CALC" = "*" ]
then
	:
fi

# Division.
if [ "$CALC" = "/" ]
then
	:
fi

Last login: Mon Nov  5 08:06:19 on ttys000
AMIGA:amiga~> cd Desktop/Code/Shell
AMIGA:amiga~/Desktop/Code/Shell> ./calc 1234567.987654321 - -1234567.135790864
+2469135.123445185
AMIGA:amiga~/Desktop/Code/Shell> python
Python 2.7.10 (default, Oct  6 2017, 22:29:07) 
[GCC 4.2.1 Compatible Apple LLVM 9.0.0 (clang-900.0.31)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> 1234567.987654321 - -1234567.135790864
2469135.123445185
>>> exit()
AMIGA:amiga~/Desktop/Code/Shell> ./calc 0.00001234567890 - 1.012401299
-1.012388953
AMIGA:amiga~/Desktop/Code/Shell> python
Python 2.7.10 (default, Oct  6 2017, 22:29:07) 
[GCC 4.2.1 Compatible Apple LLVM 9.0.0 (clang-900.0.31)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> 0.00001234567890 - 1.012401299
-1.0123889533211
>>> exit()
AMIGA:amiga~/Desktop/Code/Shell> _