R if-else语句实例图解

该语句也称为嵌套if-else语句。 if语句后面是可选的else if ….. else语句。该语句用于在单个if …… else if语句中测试各种条件。当我们使用if …. else if ….. else语句时, 需要牢记一些关键点。这些要点如下：

1. if语句可以为零或一个else语句, 并且必须在其他if语句之后。
2. if语句可以包含许多其他if语句, 它们位于else语句之前。
3. 一旦else if语句成功, 将不会测试其余的if if else。

If-else语句的基本语法如下：

if(boolean_expression 1) {
   // This block executes when the boolean expression 1 is true.
} else if( boolean_expression 2) {
   // This block executes when the boolean expression 2 is true.
} else if( boolean_expression 3) {
   // This block executes when the boolean expression 3 is true.
} else {
   // This block executes when none of the above condition is true. 
}

流程图

例子1

age <- readline(prompt="Enter age: ")
age <- as.integer(age)
if(age<18)
	print("You are child")
else if(age>30)
	print("You are old guy")
else
	print("You are adult")

输出

例子2

marks=83;
if(marks>75){
	print("First class")
}else if(marks>65){
	print("Second class")
}else if(marks>55){
	print("Third class")
}else{
	print("Fail")
}

输出

例子3

cat("1) For Addition\n")
cat("2) For Subtraction\n")
cat("3) For Division\n")
cat("4) For multiplication\n")
n1<-readline(prompt="Enter first number:")
n2<-readline(prompt="Enter second number:")
choice<-readline(prompt="Enter your choice:")
n1<- as.integer(n1)
n2<- as.integer(n2)
choice<- as.integer(choice)
if(choice==1){
	sum <-(n1+n2)
	cat("sum=", sum)
}else if(choice==2){
	sub<-(n1-n2)
	cat("sub=", sub)
}else if(choice==3){
	div<-n1/n2
	cat("Division=", div)
}else if(choice==4){
	mul<-n1*n2
	cat("mul=", mul)
}else{
	cat("wrong choice")
}

输出

例子4

x <- c("Hardwork", "is", "the", "key", "of", "success")
if("Success" %in% x) {
   print("success is found in the first time")
} else if ("success" %in% x) {
   print("success is found in the second time")
} else {
   print("No success found")
}

输出

例子5

n1=4
n2=87
n3=43
n4=74
if(n1>n2){
	if(n1>n3&&n1>n4){
		largest=n1
	}
}else if(n2>n3){
	if(n2>n1&&n2>n4){
		largest=n2
	}
}else if(n3>n4){
	if(n3>n1&&n3>n2){
		largest=n3
	}
}else{
	largest=n4
}
cat("Largest number is =", largest)

输出