I have 2 objects. DonLocation - it stores donor's username and its location (using geolocation)

ReqLocation - it stores hospital's username and its location. It stores location in 2 formats..one of them uses geolocation while other uses decimal fields to store latitude and longitude.

I am finding distance from certain hospital towards all donors. For that I am creating list of donors using SOQL query. Using for loop I am calculating distance for all donors.

But I facing many errors working with GEOLOCATION and DISTANCE function. Can anybody help me to solve this problem?

Here I am posting objects' structure and Code of controller class. Code Statement and error occuring for that statement is posted within comments.

Object 'DonLocation' structure  Object API name - DonLocation__c

Field Label                            API Name                          Data Type

DonorPlace                          DonorPlace__c                Geolocation

Username                            Username__c                  Text(20)

Object 'ReqLocation' structure  Object API name - ReqLocation__c

Field Label                             API Name                          Data Type

HospLat                                 HospLat__c                       Number(4, 14)

HospLocation                      HospLocation__c             Geolocation

HospLong                             HospLong__c                    Number(4, 14)

Username                            Username__c                    Text(20)

Controller class "NearestDonors" Code with comments

public class NearestDonors{
    public DonLocation__c dloc {get; set;}
    public ReqLocation__c hloc {get;set;}
    public double temp {get;set;}
    public double tempdouble {get;set;}
    public double tempnum {get;set;}
    public decimal tempdeci1 {get;set;}
    public decimal tempdeci2 {get;set;}
  // public location hgeo {get; set;}  Error: Compile Error: Invalid type: location at line 9 column 11
    
 public NearestDonors(){
    map<string, double> distances = new map<string, double>();

    hloc.HospLocation__Latitude__s=18.50134;
    hloc.HospLocation__Longitude__s=73.84113;

    
    List<DonLocation__c> dloclist = [select Username__c, DonorPlace__c from DonLocation__c];
  
    if ((dloclist.size()) > 0) 
    {
     for(DonLocation__c d : dloclist)
     {
         distances.put(d.Username__c,temp);
    /*tempnum = DISTANCE(GEOLOCATION(hloc.HospLat__c,hloc.HospLong__c),GEOLOCATION(d.DonorPlace__Latitude__s,d.DonorPlace__Longitude__s), 'km');
      Error: Compile Error: Method does not exist or incorrect signature: GEOLOCATION(Decimal, Decimal) at line 23 column 26*/
      
    /*tempdeci1=d.DonorPlace__Latitude__s;
      tempdeci2=d.DonorPlace__Longitude__s;
      tempnum = DISTANCE(GEOLOCATION(tempdeci1,tempdeci2),GEOLOCATION(hloc.HospLocation__Latitude__s,hloc.HospLocation__Longitude__s), 'km');
      Error: Compile Error: Method does not exist or incorrect signature: GEOLOCATION(Decimal, Decimal) at line 30 column 24*/

    /*tempnum = DISTANCE(GEOLOCATION(hloc.HospLocation__Latitude__s,hloc.HospLocation__Longitude__s),GEOLOCATION(d.DonorPlace__Latitude__s,d.DonorPlace__Longitude__s),'km');
     Error: Compile Error: Method does not exist or incorrect signature: GEOLOCATION(Decimal, Decimal) at line 33 column 26 */
    
    /*temp = DISTANCE(d.DonorPlace__c,GEOLOCATION(hloc.HospLocation__Latitude__s,hloc.HospLocation__Longitude__s), 'km');
      Error: Compile Error: Data type not supported at line 36 column 23*/
      
    /*temp=DISTANCE(d.DonorPlace__c, hloc.HospLocation__c, 'mi');
      Error: Compile Error: Data type not supported at line 39 column 21 */
      

    /*tempdouble = distance(DonorPlace__c,geolocation(hloc.HospLocation__Latitude__s,hloc.HospLocation__Longitude__s), 'km');
      Error: Compile Error: Variable does not exist: DonorPlace__c at line 43 column 29*/
      
      distances.put(d.Username__c,temp);
     
     }
    
    }
        }
}

Can anybody help me to resolve this error? Thanks in advance..