Variable value with Error Message

Question

Hi

 I am using Sap b1 Hana Database . I have below code . I want to display v_DpmBal value with error message . If i try like below i am getting error Invalid Number.

error_message:= 'Please select Down Payment Entries. Down Payment Balance : '  + v_DpmBal; 

IF (:v_DpmBal  > 0 And :v_DpmAmnt = 0)
       THEN
	        error:= v_DpmBal;                          
  			error_message:= 'Please select Down Payment Entries. Down Payment Balance : ' ;
      END IF; 

Thanks