if...else statement

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)

Swift 4中if...else语句的语法如下 -

if boolean_expression {
   /* statement(s) will execute if the boolean expression is true */
} else {
   /* statement(s) will execute if the boolean expression is false */
}

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

例子 (Example)

var varA:Int = 100;
/* Check the boolean condition using if statement */
if varA < 20 {
   /* If condition is true then print the following */
   print("varA is less than 20");
} else {
   /* If condition is false then print the following */
   print("varA is not less than 20");
}
print("Value of variable varA is \(varA)");

编译并执行上述代码时，会产生以下结果 -

varA is not less than 20
Value of variable varA is 100