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直接上代码了，注释用英文标注的，可能表示有误，是为了练习英文注释的习惯。

#include <stdio.h>
/**
 *  import how many students in class.
 *
 *  @return the students' number.
 */
int studentNum(){
    int num;
    printf("please import the student's number:\n");
    scanf("%d",&num);
    return num;
}
/**
 *  import the every student;'s score.
 *
 *  @param a          put student's score in a array.
 *  @param studentNum number of student
 */
void importScore(int a[],int studentNum){
    for (int i=0; i<studentNum; i++) {
        printf("please import the %d's student's score:\n",i+1);
        scanf("%d",&a[i]);
    }
}
/**
 *  caculate student's score of total.
 *
 *  @param a          put student's score in a array.
 *  @param studentNum number of student
 *
 *  @return student's score of total.
 */
int scoreSum(int a[],int studentNum){
    int sum = 0;
    for (int i=0; i<studentNum; i++) {
        sum  = a[i]+sum;
    }
    return sum;
}
/**
 *  caculate the student's score of average.
 *
 *  @param sum        the student's score of total.
 *  @param studentNum number of student.
 */
void scoreAverage(int sum,int studentNum){
    int average = sum/studentNum;
    printf("the student's average is %d\n",average);
}

int main(){
    int number = studentNum();
    int a[number];
    int sum;
    importScore(a, number);
    sum = scoreSum(a, number);
    scoreAverage(sum, number);
}