IndexOf和SIN

Question

我正在构建一个计算器，但如果我没有“罪”左边的任何东西，我就得不到输出。但是，如果我把数字放在“罪”之前，那么它将执行操作，并将数字的错误告诉我。我希望它能够给你一个数字的罪，即使把它作为......“sin43”

    import java.util.Scanner;

    public class InputScanner_operations {
    public static void main(String[] args) {
    Scanner input = new Scanner(System.in);
    String str;

    System.out.println("Input your equation");

    str = input.nextLine();

    int X = str.indexOf("X");
    int x = str.indexOf("x");
    int div = str.indexOf("/");
    int plu = str.indexOf("+");
    int sub = str.indexOf("-");
    int sin = str.indexOf("s");

    int type = 0;

    if (X != -1)
        type = 1;
    else if (x != -1)
        type = 2;
    else if (div != -1)
        type = 3;
    else if (plu != -1)
        type = 4;
    else if (sub != -1)
        type = 5;
    else if (sin != -1)
        type = 6;
    else
        type = 0;

    switch (type) {

    case 1: {
        int pos = str.indexOf("X");
        for (int i = 1; i <= pos; i++) {

            String upToNCharacters = str.substring(0,
                    Math.min(str.length(), i));
            String downToNCharacters = str.substring(pos + 1,
                    Math.max(str.length(), i));

            if (i == pos) {

                Double left = Double.parseDouble(upToNCharacters);
                Double right = Double.parseDouble(downToNCharacters);
                System.out.println(left * right);
            }
        }
    }
        break;
    case 2: {
        int pos = str.indexOf("x");
        for (int i = 1; i <= pos; i++) {

            String upToNCharacters = str.substring(0,
                    Math.min(str.length(), i));
            String downToNCharacters = str.substring(pos + 1,
                    Math.max(str.length(), i));

            if (i == pos) {

                Double left = Double.parseDouble(upToNCharacters);
                Double right = Double.parseDouble(downToNCharacters);
                System.out.println(left * right);
            }
        }
    }
        break;
    case 3: {
        int pos = str.indexOf("/");
        for (int i = 1; i <= pos; i++) {

            String upToNCharacters = str.substring(0,
                    Math.min(str.length(), i));
            String downToNCharacters = str.substring(pos + 1,
                    Math.max(str.length(), i));

            if (i == pos) {

                Double left = Double.parseDouble(upToNCharacters);
                Double right = Double.parseDouble(downToNCharacters);
                System.out.println(left / right);
            }
        }
    }

        break;
    case 4: {
        int pos = str.indexOf("+");
        for (int i = 1; i <= pos; i++) {

            String upToNCharacters = str.substring(0,
                    Math.min(str.length(), i));
            String downToNCharacters = str.substring(pos + 1,
                    Math.max(str.length(), i));

            if (i == pos) {

                Double left = Double.parseDouble(upToNCharacters);
                Double right = Double.parseDouble(downToNCharacters);
                System.out.println(left + right);
            }
        }
    }
        break;
    case 5: {
        int pos = str.indexOf("-");
        for (int i = 1; i <= pos; i++) {

            String upToNCharacters = str.substring(0,
                    Math.min(str.length(), i));
            String downToNCharacters = str.substring(pos + 1,
                    Math.max(str.length(), i));

            if (i == pos) {

                Double left = Double.parseDouble(upToNCharacters);
                Double right = Double.parseDouble(downToNCharacters);
                System.out.println(left - right);
            }
        }
    }
    case 6: {
        int pos = str.indexOf("s");
        for (int i = 1; i <= pos; i++) {
            String upToNCharacters = str.substring(0,
                    Math.min(str.length(), i));
            String downToNCharacters = str.substring(pos + 3,
                    Math.max(str.length(), i));

            if (i == pos) {

            @SuppressWarnings("unused")
            Double left = Double.parseDouble(upToNCharacters);
            Double right = Double.parseDouble(downToNCharacters);
            System.out.println(Math.sin(right));
            }
        }
    }
        break;
    default:
        System.out.println("Please check your formatting");

        }
    }
}

Answer 1

在这段代码中：

case 6: {
    int pos = str.indexOf("s");
    for (int i = 1; i <= pos; i++) {

您找到"s"的索引，然后开始for循环。但是如果sin位于开头，则pos将为0而不是1，因此您的for循环将永远不会执行。请记住，String的编号为0。

尝试在int i = 0循环中将其更改为int i = 1而不是for。