The first input array is the key to the correct answers to an exam, like ["a", "a", "b", "d"]. The second one contains a student's submitted answers. 
The two arrays are not empty and are the same length. Return the score for this array of answers, giving +4 for each correct answer, -1 for each incorrect answer, and +0 for each blank answer, represented as an empty string (in C the space character is used).
If the score < 0, return 0.
For example:
```
checkExam(["a", "a", "b", "b"], ["a", "c", "b", "d"]) → 6
checkExam(["a", "a", "c", "b"], ["a", "a", "b",  ""]) → 7
checkExam(["a", "a", "b", "c"], ["a", "a", "b", "c"]) → 16
checkExam(["b", "c", "b", "a"], ["",  "a", "a", "c"]) → 0
```
def check_exam(arr1,arr2):
    score = 0
    for i in range(0, 4):
        if arr1[i] == arr2[i]:
            score += 4
        elif arr2[i] == "":
            score += 0
        else:
            score -= 1
    if score > 0:    
            return score 
    else:
        return 0

def check_exam(arr1,arr2):
    score = 0
    for i in range(0, 4):
        if arr1[i] == arr2[i]:
            score += 4
        elif arr2[i] == "":
            score += 0
        else:
            score -= 1
    if score > 0:    
            return score 
    else:
        return 0
