How to combine two strings to complete a path?

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C++

Visual-Studio

VisualC++

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I am trying to combine two strings in order to complete a path to a file, but I encountered 100s of errors trying to accomplish that, I am a new C++ programmer, because I program mainly on VB.net. See, VB.net has limitations so I decided to modify a program that is written in C++ because it cannot be converted to Vb.net.
Here are the codes of a program called ClamAVGUI, it is a old GUI for the antivirus programm ClamWin. this is the CPP file of the project, it is just an exceprt. I am trying to do is this, The program has checkboxes, each
checkboxes has a command, like for example, If i checked a box named, "Log the Scan" the program will append to the CLI exe, the ff. clamscan.exe "--log=PATH TO LOG FILE", this is what I am trying to d now,
but I need to find the program on where it is, for example finding its %HOMEDRIVE% where it is installed, for ex. at drive "C:\", then I will add the ff. commands to make the program work,
GetEnvironmentValue("homedrive") += """\\ClamAV\\Logs\\logfile.log", but I cannot do this in C++. Please help me, and guide me, I've trying this for hours and still no conclusion.
I don't know if this is a MFC app, I don't how to idenfity C++ program types, please guide me. Thank You.

std::string cmdArg;
std::string strcmd1 = "--log=";
std::string strcmd2 =  GetEnvironmentValue("HOMEDRIVE");
std::string strcmd3 = "\CLamAV\logs\Scan.log";
cmdArg.append(strcmd1);
cmsArg.append(strcmd2);
cmdArg.append(strcmd3); //ERR here


const char * GetEnvironmentValue(const char * name)
{
    const DWORD buffSize = 65535;
    static char buffer[buffSize];
    if (GetEnvironmentVariableA(name, buffer, buffSize))
    {
        return buffer;
    }
    else
    {
        return 0;
    }
}

static Option options[] =
		
{

    { "--recursive",             IDC_RECURSE         },
    { "--remove",       IDC_RADIO1          },
    { "-i",             IDC_ONLYINFECTED    },

    { "--no-summary ",      IDC_NOSUMMARY          },
    { "--bell",        IDC_BEEP            },
	{ " ",        IDC_REPORT            },
	{ "--database="".\\db""",        IDC_db            }, // I need to do it here two, ex.  "--database=" & GetEnvironmentValue("HOMEDRIVE") += "\CLamAV\database" still no luck
	{"--log=" +=  GetEnvironmentValue("HOMEDRIVE") += "\CLamAV\logs\Scan.log", IDC_LOGSCAN}, //CAN'T GET THIS TO WORK... Tried 100 Times... I just need to add the proper file location so there won't be any error but, it throws an error when compiling.
	/*In VB.net If I am going to combine two strings it is easy as:   
	Dim pathoffolder as string = "C:\windows"
	Dim pathoffile as sting = "\cmd.exe"
	Msgbox(pathoffolder & pathoffile)
	Process.Start(pathoffolder & pathoffile, "arguments")
	I don't know how to do it in C++, VC++.*/
	
	  { NULL, 0 }
	};

-------------------------------UPDATED----------------------------------
Okay I managed to combine two strings by using the ff code:

char testString1[200];
char testString2[100];
            strcpy(testString2,buffer); //Second String
            strcpy(testString1,"--tempdir="""); // first string
            strcat(testString1, testString2);
//combined string would be testString1

static Option options[] =
		
{
//...
};

Then another problem arises, ERROR: IntelliSense: this declaration has no storage class or type specifier

I cannot paste it outside, but I can if it is in a another function.