此语句也称为嵌套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:
- if 语句可以包含零个或一个 else 语句，并且必须在任何 else if的语句之后。
- if 语句可以有许多 else if 语句，它们位于else语句之前。
- 一旦 else if 语句成功，将不会测试其余的 else if 或 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("Learnfk","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("THE LEARNFK.COM Largest number is =",largest)
输出:
