I am using Stack class to calculate simple arithmetic expressions involving integers, such as 1+2*3.your program would execute operations in the order given,without regarding to the precedence of operators. *Thus, the expression 1+2*3 should be calculated (1+2)*3=9,not 1+(2*3)=7.
If i get the input as 1+2*3,i know how to convert the string 1,2,3 to Integer.but i don't know how to covert +,* from string type to operator.
My code logic is: For eg: Given string 2 + (3 * 5), So 3 * 5 will be operated first then +2 will be performed in result of 3 * 5.
5 Answers
probably the best way to do it will be equals, but it's best to ignore whitespaces:
i'm not quite sure how you split your string, but for example, if you have a char op and two integer a and b:
String str = op.replace(" ", "");
if(str.equals("*")){
retVal = a*b;
} else if(str.equals("+")){
retVal = a+b;
}//etc
Do what Ogen suggested and manually check the operator. A quick shortcut to doing the if, else if .... structure is switch, that is
switch(operand) {
case "*":
break;
case "+":
break;
.....
default:
}
You will have to manually check and assign the operator. E.g.
if (s.equals("+")) {
// addition
}
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ScriptEngineManager manager = new ScriptEngineManager();
ScriptEngine se = manager.getEngineByName("JavaScript");
try {
Object result = se.eval(val);
System.out.println(result.toString());
} catch (ScriptException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
Ok, assuming your assignment needs you to use the Stack class and you already have the logic to pick numbers ( including the negative numbers -- that would an operator followed by another operator in all but one cases) and operators and parens, what you could do is as follows.
If you encounter a number, pop the last two elements from your stack. The first item you pop will be an operator and the next will be a number. Evaluate the expression and push it into Stack and continue.
You can ignore the parenthesis. You will also have to handle the case of reading a number or parenthesis the first time.
