Access database connectivity in C++ - c++

Question

I am trying to connect MS access database in C++ using C-Free 5.0 compiler. I found the following code from internet but it is giving me an error as:
[Error] C:\Users\rubeea\Documents\C-Free\Temp\db.cpp:25: error: invalid conversion from const char*' tounsigned char*'
Here's the code:
#include<windows.h>
#include<sqlext.h>
#include<stdio.h>
#include <sql.h>
int main(void){
char szDSN[256] = "Driver=std;DSN='';DBQ=E:\\student.mdb;";
/* Data Access Method used in this sample */
const char* DAM = "Direct ODBC";
HENV hEnv;
HDBC hDbc;
/* ODBC API return status */
RETCODE rc;
int iConnStrLength2Ptr;
char szConnStrOut[256];
unsigned char* query ="SELECT faculty.[name], faculty.[remarks] FROM faculty;";
SQLCHAR chval1[128], chval2[128], colName[128];
int ret1;
int ret2;
/* Number of rows and columns in result set */
SQLINTEGER rowCount = 0;
SQLSMALLINT fieldCount = 0, currentField = 0;
HSTMT hStmt;
/* Allocate an environment handle */
rc = SQLAllocEnv(&hEnv);
/* Allocate a connection handle */
rc = SQLAllocConnect(hEnv, &hDbc);
/* Connect to the 'student.accdb' database */
rc = SQLDriverConnect(hDbc, NULL, (unsigned char*)szDSN,
SQL_NTS, (unsigned char*)szConnStrOut,
255, (SQLSMALLINT*)&iConnStrLength2Ptr, SQL_DRIVER_NOPROMPT);
if (SQL_SUCCEEDED(rc))
{
printf("%s: Successfully connected to database. Data source name: \n %s\n",
DAM, szConnStrOut);
/* Prepare SQL query */
printf("%s: SQL query:\n %s\n", DAM, query);
rc = SQLAllocStmt(hDbc,&hStmt); rc = SQLPrepare(hStmt, query, SQL_NTS);
/* Bind result set columns to the local buffers */
rc = SQLBindCol(hStmt, 1, SQL_C_CHAR, chval1, 128, (SQLINTEGER*)&ret1);
rc = SQLBindCol(hStmt, 2, SQL_C_CHAR, chval2, 128, (SQLINTEGER*)&ret2);
/* Execute the query and create a record set */
rc = SQLExecute(hStmt);
if (SQL_SUCCEEDED(rc))
{
printf("%s: Retrieve schema info for the given result set:\n", DAM);
SQLNumResultCols(hStmt, &fieldCount);
if (fieldCount > 0)
{
for (currentField=1; currentField <= fieldCount; currentField++)
{
SQLDescribeCol(hStmt, currentField,
colName, sizeof(colName), 0, 0, 0, 0, 0);
printf(" | %s", colName);
}
printf("\n");
}
else
{
printf("%s: Error: Number of fields in the result set is 0.\n", DAM);
}
printf("%s: Fetch the actual data:\n", DAM);
/* Loop through the rows in the result set */
rc = SQLFetch(hStmt);
while (SQL_SUCCEEDED(rc))
{
printf(" | %s | %s\n", chval1, chval2);
rc = SQLFetch(hStmt);
rowCount++;
};
printf("%s: Total Row Count: %d\n", DAM, rowCount);
rc = SQLFreeStmt(hStmt, SQL_DROP);
}
}
else
{`enter code here`
printf("%s: Couldn't connect to %s.\n", DAM, szDSN);
}
/* Disconnect and free up allocated handles */
SQLDisconnect(hDbc);
SQLFreeHandle(SQL_HANDLE_DBC, hDbc);
SQLFreeHandle(SQL_HANDLE_ENV, hEnv);
printf("%s: Cleanup. Done.\n", DAM);
return 0;
}