atoi() in Java

Problem: Write a function to convert an ASCII string to integer, similar to atoi() function of C++.

Solution: The solution is too simple, it’s simple checks for erroneous inputs that makes writing such a function fun.

public class AsciiToInteger {  
    
 public static void main(String\[\] args) {  
  AsciiToInteger instance \= new AsciiToInteger();  
  int x \= instance.atoi("-683");  
  System.out.println("Conversion is: " + x);  
 }  
   
 private int atoi(String number) {  
  // check for NULL or empty  
  if(number \=\= null || number.trim().length() \=\= 0) {  
   throw new IllegalArgumentException("Number cannot be null/empty.");  
  }  
   
  // create a variable to store the result  
  int result \= 0;  
     
  // trim the number  
  number \= number.trim();  
     
  // check for sign as the first character  
  boolean negate \= false;  
  char sign \= number.charAt(0);  
     
  if(sign \=\= '+' || sign \=\= '-') {  
   if(sign \=\= '-') {  
    negate \= true;  
   }  
      
   number \= number.substring(1);  
  }  
     
  int length \= number.length();  
  for(int index \= 0; index < length; index++) {  
   char digit \= number.charAt(index);  
      
   // sanitize the digit  
   if(!(digit \>\= '0' && digit <\= '9')) {  
    throw new IllegalArgumentException("Number contains characters other than digits at index " + index);  
   }  
      
   digit \= (char) (digit \- '0');  
      
   result +\= (digit \* Math.pow(10, (length \- index \- 1)));  
  }  
     
  // if negative, do it  
  if(negate) {  
   result \= 0 \- result;  
  }  
     
  // return the final result  
  return result;  
 }  
   
}

See also