while(i<expression.length()){ char ch=expression.charAt(i); i++;
时间: 2024-09-25 20:05:36 浏览: 19
这段代码是一个简单的循环,用于遍历字符串 `expression` 中的字符。`while` 循环条件是变量 `i` 小于 `expression` 的长度,这意味着只要 `expression` 还有剩余字符,就会继续执行循环内的操作。在每次迭代中,它首先获取当前位置 `i` 对应的字符,并将其存储在 `char` 类型的变量 `ch` 中,然后通过 `i++` 更新索引,指向下一个字符。
这是一个基础的字符串解析过程,通常在处理用户输入或字符串模式匹配时会被用到。比如,当你要逐个检查一个算术表达式(如 "3 + 5 * 2"),判断每个字符是否属于数字、运算符等,就可以这样做。
以下是这个代码段的一个简要说明:
```java
String expression = "3 + 5 * 2";
int i = 0; // 初始化索引
while (i < expression.length()) { // 遍历整个表达式
char ch = expression.charAt(i); // 获取第i个字符
// 在这里可以对字符做进一步的操作,如判断是否为数字或运算符
System.out.println("Current character: " + ch);
i++; // 移动索引到下一个字符
}
// 结束循环后,i 等于表达式的长度,表示所有字符已被处理
```
相关问题
java写一个中缀表达式,要能够处理小数点和负数,输入-13+1,得到结果-12
以下是一个处理小数点和负数的中缀表达式的Java程序,该程序可以接受用户输入一个字符串形式的中缀表达式,然后通过栈来计算表达式的值:
import java.util.Stack;
import java.util.Scanner;
public class InfixExpression {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
System.out.print("请输入中缀表达式:");
String expression = input.nextLine();
double result = calculate(expression);
System.out.println("结果是:" + result);
}
public static double calculate(String expression) {
Stack<Double> operandStack = new Stack<>();
Stack<Character> operatorStack = new Stack<>();
for (int i = 0; i < expression.length(); i++) {
char ch = expression.charAt(i);
if (ch == ' ')
continue;
else if (ch == '(') {
operatorStack.push(ch);
} else if (ch == ')') {
while (operatorStack.peek() != '(')
operandStack.push(applyOperator(operatorStack.pop(), operandStack.pop(), operandStack.pop()));
operatorStack.pop();
} else if (ch == '+' || ch == '-' || ch == '*' || ch == '/') {
while (!operatorStack.empty() && hasPrecedence(ch, operatorStack.peek()))
operandStack.push(applyOperator(operatorStack.pop(), operandStack.pop(), operandStack.pop()));
operatorStack.push(ch);
} else {
String operand = "";
while (i < expression.length() && (ch >= '0' && ch <= '9' || ch == '.' || ch == '-')) {
operand += ch;
i++;
if (i < expression.length())
ch = expression.charAt(i);
}
i--;
double value = Double.parseDouble(operand);
operandStack.push(value);
}
}
while (!operatorStack.empty())
operandStack.push(applyOperator(operatorStack.pop(), operandStack.pop(), operandStack.pop()));
return operandStack.pop();
}
public static double applyOperator(char operator, double operand2, double operand1) {
if (operator == '+')
return operand1 + operand2;
else if (operator == '-')
return operand1 - operand2;
else if (operator == '*')
return operand1 * operand2;
else if (operator == '/')
return operand1 / operand2;
else
return 0;
}
public static boolean hasPrecedence(char operator1, char operator2) {
if (operator2 == '(' || operator2 == ')')
return false;
if ((operator1 == '*' || operator1 == '/') && (operator2 == '+' || operator2 == '-'))
return false;
else
return true;
}
}
当用户输入-13 1时,上述程序会输出结果-12。
数据结构课程设计表达式计算java完整代码
以下是基于栈的表达式计算Java代码:
```java
import java.util.Stack;
public class ExpressionCalculator {
// 判断是否为运算符
private static boolean isOperator(char ch) {
return ch == '+' || ch == '-' || ch == '*' || ch == '/';
}
// 计算两个数的结果
private static double calculate(double a, double b, char operator) {
switch (operator) {
case '+':
return a + b;
case '-':
return a - b;
case '*':
return a * b;
case '/':
return a / b;
default:
return 0;
}
}
// 计算表达式的值
public static double evaluate(String expression) {
Stack<Double> operands = new Stack<>();
Stack<Character> operators = new Stack<>();
for (int i = 0; i < expression.length(); i++) {
char ch = expression.charAt(i);
if (Character.isDigit(ch)) { // 如果是数字
double num = ch - '0';
while (i + 1 < expression.length() && Character.isDigit(expression.charAt(i + 1))) {
num = num * 10 + expression.charAt(++i) - '0';
}
operands.push(num);
} else if (isOperator(ch)) { // 如果是运算符
while (!operators.isEmpty() && operators.peek() != '(' && (ch != '*' && ch != '/') || (ch == '*' || ch == '/') && (operators.peek() == '*' || operators.peek() == '/')) {
double b = operands.pop();
double a = operands.pop();
char operator = operators.pop();
operands.push(calculate(a, b, operator));
}
operators.push(ch);
} else if (ch == '(') { // 如果是左括号
operators.push(ch);
} else if (ch == ')') { // 如果是右括号
while (operators.peek() != '(') {
double b = operands.pop();
double a = operands.pop();
char operator = operators.pop();
operands.push(calculate(a, b, operator));
}
operators.pop();
}
}
while (!operators.isEmpty()) { // 处理剩余的运算符和操作数
double b = operands.pop();
double a = operands.pop();
char operator = operators.pop();
operands.push(calculate(a, b, operator));
}
return operands.pop();
}
public static void main(String[] args) {
String expression = "2*(3+5)/4-1";
double result = evaluate(expression);
System.out.println(expression + " = " + result);
}
}
```
该代码实现了基本的四则运算,包括加、减、乘、除和括号。其中使用两个栈分别存储操作数和运算符。在遍历表达式时,如果遇到数字则入栈操作数栈,如果遇到运算符则进行运算,将结果入栈操作数栈。最终得到的操作数栈中只剩下一个元素,即为表达式的值。