java - if 语句中的变量递增

Question

这是一段代码(else 子句):

else { // for operators
            int count = 1;
            if (sub.compareTo("+") == 0){ //if + operator
                double d1=stack.pop();
                double d2=stack.pop();
                answer=d1+d2;
               //first two items on stack added
                stack.put(answer); // put ans on stack
               System.out.println(count+ ") "+d1+ " + " +d2 + " = " +answer); // display ans
               count++;
            }
            if (sub.compareTo("-") == 0){ //if - operator
                double d1=stack.pop(); //pop first two items on stack
                double d2=stack.pop();
                answer =d2-d1; //subtract the items
                stack.put(answer);//put ans on stack
                System.out.println(count+ ") "+d2+ " - " +d1 + " = " +answer);///display answer
                count++;
            }
}

此代码尝试使用 stack 来评估基本数学运算。例子有:

1. 2 + 2 = 4
2. 4 + 4 = 8

我想使用count变量来显示数字，但它保持为 1。你知道为什么吗？

Answer 1

创建您的 count 全局变量并在函数外部声明它以正确存储值，您所做的是限制 count 的范围，这就是为什么他每次都给您相同的答案

int count=1;  // make sure you count is outside your function 
else{ // for operators

            if(sub.compareTo("+")==0){ //if + operator
                double d1=stack.pop();
                double d2=stack.pop();
                answer=d1+d2;
               //first two items on stack added
                stack.put(answer); // put ans on stack
               System.out.println(count+ ") "+d1+ " + " +d2 + " = " +answer); // display ans
               count++;
            }
            if(sub.compareTo("-")==0){ //if - operator
                double d1=stack.pop(); //pop first two items on stack
                double d2=stack.pop();
                answer =d2-d1; //subtract the items
                stack.put(answer);//put ans on stack
                System.out.println(count+ ") "+d2+ " - " +d1 + " = " +answer);///display answer
                count++;
            }