Measuring WiFi signal strengh?

Use Code Bellow it will work fine
#define UNICODE

#include <windows.h>
#include <wlanapi.h>
#include <objbase.h>
#include <wtypes.h>

#include <stdio.h>
#include <stdlib.h>

// Need to link with Wlanapi.lib and Ole32.lib
#pragma comment(lib, "wlanapi.lib")
#pragma comment(lib, "ole32.lib")


int wmain()
{

// Declare and initialize variables.

HANDLE hClient = NULL;
DWORD dwMaxClient = 2; //
DWORD dwCurVersion = 0;
DWORD dwResult = 0;
DWORD dwRetVal = 0;
int iRet = 0;

WCHAR GuidString[39] = {0};

unsigned int i, j, k;

/* variables used for WlanEnumInterfaces */

PWLAN_INTERFACE_INFO_LIST pIfList = NULL;
PWLAN_INTERFACE_INFO pIfInfo = NULL;

PWLAN_AVAILABLE_NETWORK_LIST pBssList = NULL;
PWLAN_AVAILABLE_NETWORK pBssEntry = NULL;

dwResult = WlanOpenHandle(dwMaxClient, NULL, &dwCurVersion, &hClient);
if (dwResult != ERROR_SUCCESS) {
wprintf(L"WlanOpenHandle failed with error: %u\n", dwResult);
return 1;
// You can use FormatMessage here to find out why the function failed
}

dwResult = WlanEnumInterfaces(hClient, NULL, &pIfList);
if (dwResult != ERROR_SUCCESS) {
wprintf(L"WlanEnumInterfaces failed with error: %u\n", dwResult);
return 1;
// You can use FormatMessage here to find out why the function failed
} else {
wprintf(L"Num Entries: %lu\n", pIfList->dwNumberOfItems);
wprintf(L"Current Index: %lu\n", pIfList->dwIndex);
for (i = 0; i < (int) pIfList->dwNumberOfItems; i++) {
pIfInfo = (WLAN_INTERFACE_INFO *) &pIfList->InterfaceInfo[i];
wprintf(L" Interface Index[%u]:\t %lu\n", i, i);
iRet = StringFromGUID2(pIfInfo->InterfaceGuid, (LPOLESTR) &GuidString,
sizeof(GuidString)/sizeof(*GuidString));
// For c rather than C++ source code, the above line needs to be
// iRet = StringFromGUID2(&pIfInfo->InterfaceGuid, (LPOLESTR) &GuidString,
// sizeof(GuidString)/sizeof(*GuidString));
if (iRet == 0)
wprintf(L"StringFromGUID2 failed\n");
else {
wprintf(L" InterfaceGUID[%d]: %ws\n",i, GuidString);
}
wprintf(L" Interface Description[%d]: %ws", i,
pIfInfo->strInterfaceDescription);
wprintf(L"\n");
wprintf(L" Interface State[%d]:\t ", i);
switch (pIfInfo->isState) {
case wlan_interface_state_not_ready:
wprintf(L"Not ready\n");
break;
case wlan_interface_state_connected:
wprintf(L"Connected\n");
break;
case wlan_interface_state_ad_hoc_network_formed:
wprintf(L"First node in a ad hoc network\n");
break;
case wlan_interface_state_disconnecting:
wprintf(L"Disconnecting\n");
break;
case wlan_interface_state_disconnected:
wprintf(L"Not connected\n");
break;
case wlan_interface_state_associating:
wprintf(L"Attempting to associate with a network\n");
break;
case wlan_interface_state_discovering:
wprintf(L"Auto configuration is discovering settings for the network\n");
break;
case wlan_interface_state_authenticating:
wprintf(L"In process of authenticating\n");
break;
default:
wprintf(L"Unknown state %ld\n", pIfInfo->isState);
break;
}
wprintf(L"\n");

dwResult = WlanGetAvailableNetworkList(hClient,
&pIfInfo->InterfaceGuid,
0,
NULL,
&pBssList);

if (dwResult != ERROR_SUCCESS) {
wprintf(L"WlanGetAvailableNetworkList failed with error: %u\n",
dwResult);
dwRetVal = 1;
// You can use FormatMessage to find out why the function failed
} else {
wprintf(L"WLAN_AVAILABLE_NETWORK_LIST for this interface\n");

wprintf(L" Num Entries: %lu\n\n", pBssList->dwNumberOfItems);

for (j = 0; j < pBssList->dwNumberOfItems; j++) {
pBssEntry =
(WLAN_AVAILABLE_NETWORK *) & pBssList->Network[j];

wprintf(L" Profile Name[%u]: %ws\n", j, pBssEntry->strProfileName);

wprintf(L" SSID[%u]:\t\t ", j);
if (pBssEntry->dot11Ssid.uSSIDLength == 0)
wprintf(L"\n");
else {
for (k = 0; k < pBssEntry->dot11Ssid.uSSIDLength; k++) {
wprintf(L"%c", (int) pBssEntry->dot11Ssid.ucSSID[k]);
}
wprintf(L"\n");
}

wprintf(L" BSS Network type[%u]:\t ", j);
switch (pBssEntry->dot11BssType) {
case dot11_BSS_type_infrastructure :
wprintf(L"Infrastructure (%u)\n", pBssEntry->dot11BssType);
break;
case dot11_BSS_type_independent:
wprintf(L"Infrastructure (%u)\n", pBssEntry->dot11BssType);
break;
default:
wprintf(L"Other (%lu)\n", pBssEntry->dot11BssType);
break;
}

wprintf(L" Number of BSSIDs[%u]:\t %u\n", j, pBssEntry->uNumberOfBssids);

wprintf(L" Connectable[%u]:\t ", j);
if (pBssEntry->bNetworkConnectable)
wprintf(L"Yes\n");
else
wprintf(L"No\n");

wprintf(L" Signal Quality[%u]:\t %u\n", j, pBssEntry->wlanSignalQuality);

wprintf(L" Security Enabled[%u]:\t ", j);
if (pBssEntry->bSecurityEnabled)
wprintf(L"Yes\n");
else
wprintf(L"No\n");

wprintf(L" Default AuthAlgorithm[%u]: ", j);
switch (pBssEntry->dot11DefaultAuthAlgorithm) {
case DOT11_AUTH_ALGO_80211_OPEN:
wprintf(L"802.11 Open (%u)\n", pBssEntry->dot11DefaultAuthAlgorithm);
break;
case DOT11_AUTH_ALGO_80211_SHARED_KEY:
wprintf(L"802.11 Shared (%u)\n", pBssEntry->dot11DefaultAuthAlgorithm);
break;
case DOT11_AUTH_ALGO_WPA:
wprintf(L"WPA (%u)\n", pBssEntry->dot11DefaultAuthAlgorithm);
break;
case DOT11_AUTH_ALGO_WPA_PSK:
wprintf(L"WPA-PSK (%u)\n", pBssEntry->dot11DefaultAuthAlgorithm);
break;
case DOT11_AUTH_ALGO_WPA_NONE:
wprintf(L"WPA-None (%u)\n", pBssEntry->dot11DefaultAuthAlgorithm);
break;
case DOT11_AUTH_ALGO_RSNA:
wprintf(L"RSNA (%u)\n", pBssEntry->dot11DefaultAuthAlgorithm);
break;
case DOT11_AUTH_ALGO_RSNA_PSK:
wprintf(L"RSNA with PSK(%u)\n", pBssEntry->dot11DefaultAuthAlgorithm);
break;
default:
wprintf(L"Other (%lu)\n", pBssEntry->dot11DefaultAuthAlgorithm);
break;
}

wprintf(L" Default CipherAlgorithm[%u]: ", j);
switch (pBssEntry->dot11DefaultCipherAlgorithm) {
case DOT11_CIPHER_ALGO_NONE:
wprintf(L"None (0x%x)\n", pBssEntry->dot11DefaultCipherAlgorithm);
break;
case DOT11_CIPHER_ALGO_WEP40:
wprintf(L"WEP-40 (0x%x)\n", pBssEntry->dot11DefaultCipherAlgorithm);
break;
case DOT11_CIPHER_ALGO_TKIP:
wprintf(L"TKIP (0x%x)\n", pBssEntry->dot11DefaultCipherAlgorithm);
break;
case DOT11_CIPHER_ALGO_CCMP:
wprintf(L"CCMP (0x%x)\n", pBssEntry->dot11DefaultCipherAlgorithm);
break;
case DOT11_CIPHER_ALGO_WEP104:
wprintf(L"WEP-104 (0x%x)\n", pBssEntry->dot11DefaultCipherAlgorithm);
break;
case DOT11_CIPHER_ALGO_WEP:
wprintf(L"WEP (0x%x)\n", pBssEntry->dot11DefaultCipherAlgorithm);
break;
default:
wprintf(L"Other (0x%x)\n", pBssEntry->dot11DefaultCipherAlgorithm);
break;
}

wprintf(L"\n");
}
}
}

}
if (pBssList != NULL) {
WlanFreeMemory(pBssList);
pBssList = NULL;
}

if (pIfList != NULL) {
WlanFreeMemory(pIfList);
pIfList = NULL;
}

return dwRetVal;
}