switch (operators.get(i))
时间: 2024-09-19 18:09:58 浏览: 19
这是一个Java语言中的`switch`语句,主要用于根据不同值执行不同的代码块。`operators.get(i)`这部分是一个表达式,通常从一个集合(如ArrayList、HashMap等)中获取第`i`个元素,这里假设`operators`是一个包含操作符的列表(例如加法、减法、乘法等)。`get(i)`函数返回的是该位置的运算符。
`switch`结构如下:
```java
Operator operators[] = ...; // 假设有一个操作符数组
int index = i; // 可能是从用户输入或者其他地方获取的索引
switch (operators[index]) {
case "+":
// 当前操作符是加法,执行相应的代码
break;
case "-":
// 当前操作符是减法,执行相应的代码
break;
case "*":
// 当前操作符是乘法,执行相应的代码
break;
// 其他case语句可以添加,对应不同的操作符
default:
// 操作符不在上述列举中,执行默认操作或抛出异常
break;
}
```
相关问题
Write a program to evaluate a postfix expression. You only have to handle four kinds of operators: +, -, x, and /. Format of functions: ElementType EvalPostfix( char *expr ); where expr points to a string that stores the postfix expression. It is guaranteed that there is exactly one space between any two operators or operands. The function EvalPostfix is supposed to return the value of the expression. If it is not a legal postfix expression, EvalPostfix must return a special value Infinity which is defined by the judge program.
Sure, I can help you with that. Here's the implementation of the `EvalPostfix` function in C:
```c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>
#define Infinity 1e9 // special value for invalid expression
typedef double ElementType; // type of operands
typedef struct Stack {
int top; // index of the top element
int capacity; // max capacity of the stack
ElementType *array; // array to store elements
} Stack;
// function to create a new stack
Stack *CreateStack(int capacity) {
Stack *stack = (Stack *) malloc(sizeof(Stack));
stack->top = -1;
stack->capacity = capacity;
stack->array = (ElementType *) malloc(stack->capacity * sizeof(ElementType));
return stack;
}
// function to check if the stack is empty
bool IsEmpty(Stack *stack) {
return stack->top == -1;
}
// function to check if the stack is full
bool IsFull(Stack *stack) {
return stack->top == stack->capacity - 1;
}
// function to push an element onto the stack
void Push(Stack *stack, ElementType element) {
if (IsFull(stack)) {
printf("Error: Stack is full\n");
exit(EXIT_FAILURE);
}
stack->array[++stack->top] = element;
}
// function to pop an element from the stack
ElementType Pop(Stack *stack) {
if (IsEmpty(stack)) {
printf("Error: Stack is empty\n");
exit(EXIT_FAILURE);
}
return stack->array[stack->top--];
}
// function to evaluate a postfix expression
ElementType EvalPostfix(char *expr) {
Stack *stack = CreateStack(strlen(expr));
char *token = strtok(expr, " "); // get the first token
while (token != NULL) {
if (isdigit(token[0])) { // if token is an operand
Push(stack, atof(token)); // push it onto the stack
} else { // if token is an operator
// pop the top two elements from the stack
ElementType operand2 = Pop(stack);
ElementType operand1 = Pop(stack);
// perform the operation and push the result onto the stack
switch (token[0]) {
case '+':
Push(stack, operand1 + operand2);
break;
case '-':
Push(stack, operand1 - operand2);
break;
case 'x':
Push(stack, operand1 * operand2);
break;
case '/':
if (operand2 == 0) { // division by zero
return Infinity;
}
Push(stack, operand1 / operand2);
break;
default:
return Infinity; // invalid operator
}
}
token = strtok(NULL, " "); // get the next token
}
if (stack->top != 0) { // invalid expression
return Infinity;
}
return Pop(stack); // return the final result
}
int main() {
char expr[] = "5 3 2 x - 4 +";
ElementType result = EvalPostfix(expr);
if (result == Infinity) {
printf("Error: Invalid expression\n");
} else {
printf("Result = %g\n", result);
}
return 0;
}
```
In this implementation, we use a stack to store the operands and perform the operations on them. We tokenize the postfix expression using the `strtok` function and process each token one by one. If the token is an operand, we convert it to a `double` and push it onto the stack. If the token is an operator, we pop the top two elements from the stack, perform the operation, and push the result back onto the stack. If the expression is invalid, we return the special value `Infinity`.
怎么随机出现运算符java
在Java中,如果你想让程序随机地选择并执行一些基本运算符,你可以创建一个包含所有可能运算符的数组或枚举,并利用`Random`类来生成随机数来索引这个数组。下面是一个简单的示例:
```java
import java.util.Random;
public enum MathOperator {
ADD('+'),
SUBTRACT('-'),
MULTIPLY('*'),
DIVIDE('/');
private final String symbol;
MathOperator(String symbol) {
this.symbol = symbol;
}
public String getSymbol() {
return symbol;
}
}
public class RandomMath {
public static void main(String[] args) {
MathOperator[] operators = MathOperator.values();
Random random = new Random();
int index = random.nextInt(operators.length);
MathOperator operator = operators[index];
double num1 = 5.0; // 示例数字
double num2 = 3.0; // 另一示例数字
switch (operator) {
case ADD:
System.out.println(num1 + " " + operator.getSymbol() + " " + num2);
break;
case SUBTRACT:
System.out.println(num1 + " " + operator.getSymbol() + " " + num2);
break;
case MULTIPLY:
System.out.println(num1 + " " + operator.getSymbol() + " " + num2);
break;
case DIVIDE:
if (num2 != 0) { // 防止除以零错误
System.out.println(num1 + " " + operator.getSymbol() + " " + num2);
} else {
System.out.println("Error: Division by zero not allowed");
}
break;
}
}
}
```
在这个例子中,我们创建了一个`MathOperator`枚举,包含了加、减、乘、除四种操作。然后通过`random.nextInt()`生成一个随机索引,取出对应的运算符执行相应的计算。