Hi,
now I am writing a very small and simple calculator program. The user may type in a string, eg: 123 / 345, then I suppose to convert this string into integer, and then try to calculate out the output. Does anyone know how to do the conversion. Do I hv to consider the case when when divide by 0? Do we have to throws exception in this case?

Below is a small partial code i wrote to extract the individual number out
eg. 123
/
345
. But I only can manage to print out the individual number using one line per word. How do I use it to convert it to integer and then divide them together?

Code:
    //-----------------------------------------------------
    // main method 
    //-----------------------------------------------------
    public static void main (String [] args)  {
        
        //Calculator cal = new Calculator();
        
        
        //int numAdd1 = 0, numAdd2 = 0;
        int index = 0,   numberOfCharacters,
            beginIdx ,   endIdx;
        
        String word, reply = " ";
        
        Matcher matcher;
        Pattern pattern = Pattern.compile(VALID_INPUT_PATTERN);
        
        //System.out.print("");
        Scanner sc = new Scanner(System.in);
        
        String str = sc.nextLine();
        numberOfCharacters = str.length();
        
        
        while(true) {
            if (str.equals(Q)) break;
            
            if (str.matches(VALID_INPUT_PATTERN)) {
                while ( index < numberOfCharacters ) {
                    
                    //ignore leading blank spaces
                    while (index < numberOfCharacters &&
                           str.charAt(index) == BLANK) {
                        
                        index++;
                    }
                    
                    beginIdx = index;
                    
                    //now locate the end of the word
                    while (index < numberOfCharacters &&
                           str.charAt(index) != BLANK) {
                        
                        index++;
                    }
                    
                    endIdx = index;
                    
                    //System.out.println( beginIdx + "      " + endIdx );  //TEMP
                    
                    
                    if (beginIdx != endIdx) {
                        
                        //another word is found, extract it from the
                        //sentence and print it out
                        
                        word = str.substring( beginIdx, endIdx );
                        
                        System.out.println(word);
                              
                        
                    }
                }
            } else {
                //System.out.println(INVALID_INPUT);
                reply = INVALID_INPUT;
            }
            
            System.out.println(reply); break;
        }
        
        /
     
    }
}