[div]

cache get field content in a new defined variable, then compare the value

Code:

PlayerData[extraid][pExam] = cache_get_field_int(0, "Exam");

if(!PlayerData[playerid][pExam]) >=1)

//REST CODE GOES HERE
 StartExam(playerid);

So, it will only allow 1 or more than 1, not less than that.