the program runs but i still have problem for example i enter +56 and return 11 but when i tried to enter -+567 return 25 instead of 23 also when i tried to enter +45-3 it return 9 so after 5 the program stop it just return the addition of 4+5

public static int prefixEvaluation(String s){

int result=0 ;
int i=1;
char ch = s.charAt(0);
s=s.substring(i , s.length()); // i want to be able go though the entire string

if (ch>='0'&& ch<='9'){
return result;
else if (ch=='+'|| ch=='-'|| ch=='*'|| ch=='/'){
char op=ch;

int operand1= prefixEvaluation(s);

s = s.substring(i++);
int operand2= prefixEvaluation(s);
any suggestion of how to to read the string everything i call the recursive function