变量乘法 [英] Variables Multiplication

问题描述

我正在编写一个脚本，为插入的数字提供阶乘，但是我在乘法时遇到了一些问题.

I'm making a script which gives the factorial for a inserted number, but i'm having some problems with the multiplication.

注意:阶乘为:9！= 9 * 8 * 7 * 6 * 5 * 4 * 3 * 2 * 1

Note: the factorial for is given by: 9!=9*8*7*6*5*4*3*2*1

这是我的代码:

#!/bin/bash

echo "Insert an Integer"

read input

if ! [[ "$input" =~ ^[0-9]+$ ]] ; then
   exec >&2; echo "Error: You didn't enter an integer"; exit 1
fi

function factorial
{
while [ "$input" != 1 ];
do
    result=$(($result * $input))
    input=$(($input-1))
done
}
factorial
echo "The Factorial of " $input "is" $result

对于不同的乘法技术，它总是给我带来各种错误:/

it keeps giving me errors of all kinds for diferent multiplication technics :/

当前输出为:

joaomartinsrei@joaomartinsrei ~/Área de Trabalho/Shell $ ./factorial.sh
Insert an Integer
3
./factorial.sh: line 15: * 3: syntax error: operand expected (error token is "* 3")
The factorial of 3 is

非常感谢， 最好的问候

Many Thanks, Best Regards

推荐答案

主要问题是，您永远不会初始化result(至1)，因此:

The main problem is that you never initialize result (to 1), so this:

result=$(($result * $input))

等效于此:

result=$(( * $input))

这不是有效的算术表达式.

which is not a valid arithmetic expression.

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