D编程 if...else statement
if语句后面可以跟随可选的else语句，该语句在布尔表达式为false时执行。
if...else - 语法
D编程语言中if.else语句的语法是-
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，则执行代码的if块，否则执行代码的else块。
d编程语言将任何非零和非NULL值假定为TRUE，如果它是零或NULL，则假定它为FALSE值。
if...else - 流程图
if...else - 示例
import std.stdio;
int main () {
/* local variable definition */
int a=100;
/* check the boolean condition */
if( a < 20 ) {
/* if condition is true then print the following */
writefln("a is less than 20" );
} else {
/* if condition is false then print the following */
writefln("a is not less than 20" );
}
writefln("value of a is : %d", a);
return 0;
}编译并执行上述代码时，将生成以下结果-
a is not less than 20;
value of a is : 100if...elseif...else - 语句
If语句后面可以跟随可选的Else If.Else语句，这对于使用单个If.Else If语句测试各种条件非常有用。
在使用If，Else语句时，有几点需要牢记-
if可以有零个或一个其他IF，并且它必须在任何其他IF之后。
if可以有零到许多其他if，它们必须出现在else之前。
一旦Else If成功，就不会测试其余的Else If或Else。
D编程语言中if.else语句的语法是-
if(boolean_expression 1) {
/* Executes when the boolean expression 1 is true */
} else if( boolean_expression 2) {
/* Executes when the boolean expression 2 is true */
} else if( boolean_expression 3) {
/* Executes when the boolean expression 3 is true */
} else {
/* executes when the none of the above condition is true */
}if...elseif...else - 示例
import std.stdio;
int main () {
/* local variable definition */
int a=100;
/* check the boolean condition */
if( a == 10 ) {
/* if condition is true then print the following */
writefln("Value of a is 10" );
} else if( a == 20 ) {
/* if else if condition is true */
writefln("Value of a is 20" );
} else if( a == 30 ) {
/* if else if condition is true */
writefln("Value of a is 30" );
} else {
/* if none of the conditions is true */
writefln("None of the values is matching" );
}
writefln("Exact value of a is: %d", a );
return 0;
}编译并执行上述代码时，将生成以下结果-
None of the values is matching
Exact value of a is: 100