for循环没有正确遍历数组.(选择3

函数"studScore"中的for循环在输入每个学生的成绩后打印出错误的成绩字母。这不是完整的代码。在选择选项1并为学生输入成绩后。选择选项3并为每个学生输出相同的字母分数。

#include <iostream>
using namespace std;
int students;
double average;
int grade[300][6];
int score;
void letter();
double studScore();
double classave();
int stud;

int main()
{
int choice;
int choice1;
cout<< "Student project Database"<<endl<<endl<<endl;
do {
    cout<< "Please choose an option."<<endl;
    cout<< "1. To store the scores for students' quizzes. "<<endl;
    cout<< "2. To compute the class average on a specific quiz."<<endl;
    cout<< "3. To see the letter grade of a specific student."<<endl;
    cout<< "4. To compute the overall class average in the course."<<endl;
    cout<< "Press 0 to quit."<<endl;
    cout<< "Please choose: ";
    cin>> choice;
    cout<<endl;

}
while (choice!=1);
if (choice==1){
    cout<<"Please give the number of students: ";
    cin>>students;
    for (i =0; i<students;i++){
        for (j=0; j<6; j++){
            cout<<"Please give the score of student "<<(i+1)<<" in quiz "<<(j+1)<<": ";
            cin>>score;
            grade[i][j]=score;
        }
    }
        cout<<endl;
    do {
            cout<< "Please choose an option."<<endl;
            cout<< "1. To store the scores for students' quizzes. "<<endl;
            cout<< "2. To compute the class average on a specific quiz."<<endl;
            cout<< "3. To see the letter grade of a specific student."<<endl;
            cout<< "4. To compute the overall class average in the course."<<endl;
            cout<< "Press 0 to quit."<<endl;
            cout<< "Please choose: ";
            cin>> choice1;
            cout<<endl;
            if (!cin){
                cin.clear();
                cin.ignore();
                cout<<"Invalid choice. Only options 0-4 are allowed."<<endl<<endl;
            }

            else if (choice1==3){
                cout<<"Please give the student #: ";
            studScore();
            letter();
            }
            else if (choice1==4){
                cout<<"The class average is "<<c_ave;
            }
    }
        while(choice1!=0&&choice==1);
}
    return 0;}
cout<<endl;
 return average;

double studScore(){
int sum=0;
cin>>stud;
if(stud>i){
    cout<<"Invalid choice for student #"<<endl<<endl;
    return 0;
}
for(i=stud-1; i<=stud-1;i++){
    for(j=0;j<6;j++){
        sum+=grade[i][j];
        ave2=(sum/6);
    }
    return ave2;
}
}
void letter(){
if (ave2>=93&&ave2<=100)
    cout<<"The letter grade for student "<<(stud)<<" is A"<<endl<<endl;
if(ave2>=87 && ave2<93)
    cout<<"The letter grade for student "<<(stud)<<" is A-"<<endl<<endl;
if(ave2>=83&&ave2<87)
    cout<<"The letter grade for student "<<(stud)<<" is B+"<<endl<<endl;
if(ave2>=80&&ave2<83)
    cout<<"The letter grade for student "<<(stud)<<" is B"<<endl<<endl;
if(ave2>=77&&ave2<80)
    cout<<"The letter grade for student "<<(stud)<<" is B-"<<endl<<endl;
if(ave2>=73&&ave2<77)
    cout<<"The letter grade for student "<<(stud)<<" is C+"<<endl<<endl;
if(ave2>=70&&ave2<73)
    cout<<"The letter grade for student "<<(stud)<<" is C"<<endl<<endl;
if(ave2>=67&&ave2<70)
    cout<<"The letter grade for student "<<(stud)<<" is C-"<<endl<<endl;
if(ave2<67)
    cout<<"Student "<<(stud)<<" failed the course."<<endl<<endl;

}

一些示例输出

Please choose an option.
1. To store the scores for students' quizzes. 
2. To compute the class average on a specific quiz.
3. To see the letter grade of a specific student.
4. To compute the overall class average in the course.
Press 0 to quit.
Please choose: 1
Please give the number of students: 3
Please give the score of student 1 in quiz 1: 95
Please give the score of student 1 in quiz 2: 95
Please give the score of student 1 in quiz 3: 95
Please give the score of student 1 in quiz 4: 95
Please give the score of student 1 in quiz 5: 95
Please give the score of student 1 in quiz 6: 95
Please give the score of student 2 in quiz 1: 80
Please give the score of student 2 in quiz 2: 80
Please give the score of student 2 in quiz 3: 80
Please give the score of student 2 in quiz 4: 80
Please give the score of student 2 in quiz 5: 80
Please give the score of student 2 in quiz 6: 80
Please give the score of student 3 in quiz 1: 56
Please give the score of student 3 in quiz 2: 56
Please give the score of student 3 in quiz 3: 56
Please give the score of student 3 in quiz 4: 56
Please give the score of student 3 in quiz 5: 56
Please give the score of student 3 in quiz 6: 56
Please choose an option.
1. To store the scores for students' quizzes. 
2. To compute the class average on a specific quiz.
3. To see the letter grade of a specific student.
4. To compute the overall class average in the course.
Press 0 to quit.
Please choose: 3
Please give the student #: 2
The letter grade for student 2 is B
Please choose an option.
1. To store the scores for students' quizzes. 
2. To compute the class average on a specific quiz.
3. To see the letter grade of a specific student.
4. To compute the overall class average in the course.
Press 0 to quit.
Please choose: 3
Please give the student #: 3
Invalid choice for student #
The letter grade for student 3 is B