if...else statement

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2023-12-01

Perl if语句后面可以跟一个可选的else语句，该语句在布尔表达式为false时执行。

语法 (Syntax)

Perl编程语言中if...else语句的语法是 -

if(boolean_expression) {
   # statement(s) will execute if the given condition is true
} else {
   # statement(s) will execute if the given condition is false
}

如果布尔表达式的计算结果为true ，那么将执行else block代码else block ，否则将执行代码else block 。

数字0，字符串'0'和“”，空列表（）和undef在布尔上下文中都是false ，所有其他值都为true 。否定真正的价值! 或not返回特殊的假值。

流程图 (Flow Diagram)

例子 (Example)

#!/usr/local/bin/perl
$a = 100;
# check the boolean condition using if statement
if( $a < 20 ) {
   # if condition is true then print the following
   printf "a is less than 20\n";
} else { 
   # if condition is false then print the following
   printf "a is greater than 20\n";
}
print "value of a is : $a\n";
$a = "";
# check the boolean condition using if statement
if( $a ) {
   # if condition is true then print the following
   printf "a has a true value\n";
} else {
   # if condition is false then print the following
   printf "a has a false value\n";
}
print "value of a is : $a\n";

执行上述代码时，会产生以下结果 -

a is greater than 20
value of a is : 100
a has a false value
value of a is :