sum and substract using char and string only - string

Question

I have to make a code that sums and subtracts two or more numbers using the + and - chars
I managed to make the sum, but I have no idea on how to make it subtract.
Here is the code (I'm allowed to use the for and while loops only):
int CM = 0, CR = 0, A = 0, PS = 0, PR = 0, LC = 0, D;
char Q, Q1;
String f, S1;
f = caja1.getText();
LC = f.length();
for (int i = 0; i < LC; i++) {
Q = f.charAt(i);
if (Q == '+') {
CM = CM + 1;
} else if (Q == '-') {
CR = CR + 1;
}
}
while (CM > 0 || CM > 0) {
LC = f.length();
for (int i = 0; i < LC; i++) {
Q = f.charAt(i);
if (Q == '+') {
PS = i;
break;
} else {
if (Q == '-') {
PR = i;
break;
}
}
}
S1 = f.substring(0, PS);
D = Integer.parseInt(S1);
A = A + D;
f = f.substring(PS + 1);
CM = CM - 1;
}
D = Integer.parseInt(f);
A = A + D;
salida.setText("resultado" + " " + A + " " + CR + " " + PR + " " + PS);

Answer 1

The following program will solve your problem of performing addition and subtraction in a given equation in String
This sample program is given in java
public class StringAddSub {
public static void main(String[] args) {
//String equation = "100+500-20-80+600+100-50+50";
//String equation = "100";
//String equation = "500-900";
String equation = "800+400";
/** The number fetched from equation on iteration*/
String b = "";
/** The result */
String result = "";
/** Arithmetic operation to be performed */
String previousOperation = "+";
for (int i = 0; i < equation.length(); i++) {
if (equation.charAt(i) == '+') {
result = performOperation(result, b, previousOperation);
previousOperation = "+";
b = "";
} else if (equation.charAt(i) == '-') {
result = performOperation(result, b, previousOperation);
previousOperation = "-";
b = "";
} else {
b = b + equation.charAt(i);
}
}
result = performOperation(result, b, previousOperation);
System.out.println("Print Result : " + result);
}
public static String performOperation(String a, String b, String operation) {
int a1 = 0, b1 = 0, res = 0;
if (a != null && !a.equals("")) {
a1 = Integer.parseInt(a);
}
if (b != null && !b.equals("")) {
b1 = Integer.parseInt(b);
}
if (operation.equals("+")) {
res = a1 + b1;
}
if (operation.equals("-")) {
res = a1 - b1;
}
return String.valueOf(res);
}
}