# 最新Perl语言入门(第四版)习题答案

2.12 练习

1、写一个程序，计算半径为12.5的圆的周长。圆周长等于2π（π约为3.1415926）乘以半径。答案为78.5。

-----------------------/home/confish/perl/girth

#!/usr/bin/perl -w

#this program calculate a circle's girth

\$r=12.5;

\$g=12.5*2*3.1415;

print "the girth of the circle is \$g\n";

-----------------------/home/confish/perl/girth

2、修改上述程序，用户可以在程序运行时输入半径。如果，用户输入12.5，则应得到和上题一样的结果。

-----------------------/home/confish/perl/girthpro

#!/usr/bin/perl -w

#a better one to calculate girth

print"enter the radius of the circle\n";

chomp(\$r=);

if(\$r>0)

{

print"the girth of the circle is ".\$r*2*3.1415."\n";

}

else

{

print"nonavailable!\n";

}

-----------------------/home/confish/perl/girthpro

3、修改上述程序，当用户输入小于0 的数字时，程序输出的周长为0，而非负数。

-----------------------/home/confish/perl/girthzero

#!/usr/bin/perl -w

#calculate the girth and print 0 when the radius is lower than 0

print"enter the radius of the line\n";

chomp(\$r=);

if(\$r>0)

{

print"the girth of the circle is \$r*2*3.1415\n";

}

else

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