Java calculator with multiple operations
I have the following so far which works fine. Im sure there is probably an easier way to do this but what I will need to change/alter is the top method of Matheq. The Math method does the single math operations.
The it does work with any single operation with +, -, *, and /.
My problem is solving a bigger equation such as 10 - 10 / 5 + 3. It does however solve 10 / 5 + 65 * 2 properly. The reason is that each part, numbers and operations, are split to a string array. After each operation is complete the numbers and operation is replaced with the result of that equation. May seem more confusing but I couldn't think of any better way. The reason why it can't solve the other equation is because of how I mapped the strings back into string array.
Example of string arrays Ex. with 10 - 10 / 5 + 3 String = { 10, -, 10, /, 5, +, 3 } after operations does division first then left to right subtraction then addition String = { 8, 8, 2, 2, 2, 5, 5 }
Here is my code and someone please help me:
REVISED revised, now it works with above but still has some trouble with LONG equations. A short example is that it solves 2 * 2 * 2 * 2 divided by 5 just fine but if change it so 10 - 2 * 2 * 2 * 2 divided by 5 I get wrong answer.
public class Matheq {
String fnum = null;
String lnum = null;
String total = null;
public String Matheq(String mathoperation) {
String mathoperation= "6 * 3 - 4 * 2";
mathoperation = mathoperation.replaceAll(",", "");
mathoperation = mathoperation.replaceAll("plus", "+");
mathoperation = mathoperation.replaceAll("minus", "-");
mathoperation = mathoperation.replaceAll("times", "*");
mathoperation = mathoperation.replaceAll("divided by", "dividedby");
mathoperation = mathoperation.replaceAll("percent of", "percentof");
String[] splitstr = mathoperation.split(" ");
while(splitstr.length>1){
for(int i=0; i<splitstr.length; i++) {
System.out.println("Get value: " + splitstr[i]);
if(splitstr[i].indexOf("percentof") >= 0) {
String buildit = splitstr[i-1] + " percent of " + splitstr[i+1];
String done = math(buildit);
System.out.println("Percentage operation: " + splitstr[i-1] + " percent of " + splitstr[i+1] + "=" + done);
splitstr[i] = done;
splitstr[i-1] = "";
splitstr[i+1] = "";
ArrayList<String> list = new ArrayList<String>();
for(String s : splitstr){
if(!s.equals("")){
list.add(s);
}
}
splitstr = list.toArray(new String[list.size()]);
}
}
for(int i=0; i<splitstr.length; i++) {
System.out.println("Get value: " + splitstr[i]);
if(splitstr[i].indexOf("dividedby") >= 0) {
String buildit = splitstr[i-1] + " divided by " + splitstr[i+1];
String done = math(buildit);
System.out.println("Division operation: " + splitstr[i-1] + " divided by " + splitstr[i+1] + "=" + done);
splitstr[i] = done;
splitstr[i-1] = "";
splitstr[i+1] = "";
ArrayList<String> list = new ArrayList<String>();
for(String s : splitstr){
if(!s.equals("")){
list.add(s);
}
}
splitstr = list.toArray(new String[list.size()]);
}
}
for(int i=0; i<splitstr.length; i++) {
System.out.println("Get value: " + splitstr[i]);
if(splitstr[i].indexOf("*") >= 0) {
String buildit = splitstr[i-1] + " * " + splitstr[i+1];
String done = math(buildit);
System.out.println("Multiplication operation: "+ splitstr[i-1] + " * " + splitstr[i+1] + "=" + done);
splitstr[i] = done;
splitstr[i-1] = "";
splitstr[i+1] = "";
ArrayList<String> list = new ArrayList<String>();
for(String s : splitstr){
if(!s.equals("")){
list.add(s);
}
}
splitstr = list.toArray(new String[list.size()]);
}
}
for(int i=0; i<splitstr.length; i++) {
System.out.println("Get value: " + splitstr[i]);
if(splitstr[i].indexOf("+") >= 0) {
String buildit = splitstr[i-1] + " + " + splitstr[i+1];
String done = math(buildit);
System.out.println("Addition operation: " + splitstr[i-1] + " + " + splitstr[i+1] + "=" + done);
splitstr[i] = done;
splitstr[i-1] = "";
splitstr[i+1] = "";
ArrayList<String> list = new ArrayList<String>();
for(String s : splitstr){
if(!s.equals("")){
list.add(s);
}
}
splitstr = list.toArray(new String[list.size()]);
}
}
for(int i=0; i<splitstr.length; i++) {
System.out.println("Get value: " + splitstr[i]);
if(splitstr[i].indexOf("-") >= 0) {
String buildit = splitstr[i-1] + " - " + splitstr[i+1];
String done = math(buildit);
System.out.println("Subtraction operation: " + splitstr[i-1] + " - " + splitstr[i+1] + "=" + done);
splitstr[i] = done;
splitstr[i-1] = "";
splitstr[i+1] = "";
ArrayList<String> list = new ArrayList<String>();
for(String s : splitstr){
if(!s.equals("")){
list.add(s);
}
}
splitstr = list.toArray(new String[list.size()]);
}
}
for(int i=0; i<splitstr.length; i++) {
System.out.println("Final operation: " + total + " " + splitstr[i]);
}
}
return total;
}
private String math(String mathoperation) {
// TODO Auto-generated method stub
if(mathoperation.contains("percent of")){
mathoperation = mathoperation.replaceAll("percent of", "%");
int str = mathoperation.indexOf("%");
System.out.println(str);
fnum = mathoperation.substring(0, str-1);
fnum = fnum.replaceAll(" ", "");
fnum = "." + fnum;
System.out.println(fnum);
double intfnum = Double.parseDouble(fnum);
System.out.println(intfnum);
int lastind = mathoperation.length();
System.out.println(lastind);
lnum = mathoperation.substring(str+1, lastind);
lnum = lnum.replaceAll(" ", "");
System.out.println(lnum);
double intlnum = Double.parseDouble(lnum);
System.out.println(intlnum);
double tot = intlnum * intfnum;
System.out.println(tot);
total = Double.toString(tot);
if(total.length() == 3){
total = total + "0";
}
if(total.length() > 5){
total = total.substring(0, 4);
}
total = total.replace("0.", "");
System.out.println("Total:" + total);
} else
if(mathoperation.contains("-")){
int str = mathoperation.indexOf("-");
System.out.println(str);
fnum = mathoperation.substring(0, str-1);
fnum = fnum.replaceAll(" ", "");
System.out.println(fnum);
double intfnum = Double.parseDouble(fnum);
System.out.println(intfnum);
int lastind = mathoperation.length();
System.out.println(lastind);
lnum = mathoperation.substring(str+1, lastind);
lnum = lnum.replaceAll(" ", "");
System.out.println(lnum);
double intlnum = Double.parseDouble(lnum);
System.out.println(intlnum);
double tot = intfnum - intlnum;
System.out.println(tot);
total = Double.toString(tot);
System.out.println(total);
} else
if(mathoperation.contains("+")){
int str = mathoperation.indexOf("+");
System.out.println(str);
fnum = mathoperation.substring(0, str-1);
fnum = fnum.replaceAll(" ", "");
System.out.println(fnum);
double intfnum = Double.parseDouble(fnum);
System.out.println(intfnum);
int lastind = mathoperation.length();
System.out.println(lastind);
lnum = mathoperation.substring(str+1, lastind);
lnum = lnum.replaceAll(" ", "");
System.out.println(lnum);
double intlnum = Double.parseDouble(lnum);
System.out.println(intlnum);
double tot = intfnum + intlnum;
System.out.println(tot);
total = Double.toString(tot);
System.out.println(total);
} else
if(mathoperation.contains("*")){
int str = mathoperation.indexOf("*");
System.out.println(str);
fnum = mathoperation.substring(0, str-1);
fnum = fnum.replaceAll(" ", "");
System.out.println(fnum);
double intfnum = Double.parseDouble(fnum);
System.out.println(intfnum);
int lastind = mathoperation.length();
System.out.println(lastind);
lnum = mathoperation.substring(str+1, lastind);
lnum = lnum.replaceAll(" ", "");
System.out.println(lnum);
double intlnum = Double.parseDouble(lnum);
System.out.println(intlnum);
double tot = intfnum * intlnum;
System.out.println(tot);
total = Double.toString(tot);
System.out.println(total);
} else
if(mathoperation.contains("divided by")){
mathoperation = mathoperation.replaceAll("divided by", "/");
int str = mathoperation.indexOf("/");
System.out.println(str);
fnum = mathoperation.substring(0, str-1);
fnum = fnum.replaceAll(" ", "");
System.out.println(fnum);
double intfnum = Double.parseDouble(fnum);
System.out.println(intfnum);
int lastind = mathoperation.length();
System.out.println(lastind);
lnum = mathoperation.substring(str+1, lastind);
lnum = lnum.replaceAll(" ", "");
System.out.println(lnum);
double intlnum = Double.parseDouble(lnum);
System.out.println(intlnum);
double tot = intfnum / intlnum;
System.out.println(tot);
total = Double.toString(tot);
System.out.println(total);
} else {
total = null;
}
return total;
}
}
Answer
An array is the wrong structure to represent the parsed equation. You need to have a structure that can represent the operator precedence. The typical mechanism for handling this type of problem is an abstract syntax tree. For your 10 - 10 / 5 + 3 example you would probably want to build a tree that looks like this:
<result>
/ \
'-' '+'
/ \ / \
10 '/' 3
/ \
10 5
With this type of structure with the high precedence operators lower down the tree, then you can perform a bottom up evaluation to get the correct result.