public static void divideString(String str){
		char[] carr = str.toCharArray();
		int len = carr.length;
		for( int i=0; i< len-1; i++){
			char chari = carr[i];
			char nextc = carr[i+1];
			if( isDigit( chari)){
				stack.push( char2int(chari) );
			}else if(isOp(chari)){
				Op op = new Op();
				op.left = stack.peek();
				op.op = chari;
				op.right = char2int(nextc);
				ops.add(op);
			}
			if(i==len-2&& i!=0){
				stack.push( char2int(nextc));
			}
		}
		return;
	}