我的程序不断四舍五入到最接近的整数

我今天在C++实验室遇到了一个烦人的问题，我无法弄清楚。我的班级正在学习开关语句和 while 循环，并且正在研究一个输入成绩和计算平均绩点的项目。我的程序似乎进展顺利，但我无法弄清楚为什么它一直四舍五入到整数而不是显示小数点。例如，当我输入随机成绩时，它会输出 3.00 作为 GPA，而不是输出 2.76 之类的东西。我的代码仍在进行中，但是当我像教授的示例程序一样上交它时，它应该能够计算十进制数：http://classes.aligra.com/Riverside%20City%20College/2019%20Fall/CSC5/Projects/Project%2002.pdf

任何反馈将不胜感激。

#include <iostream>
#include <iomanip>
using namespace std;
/*******************************************************
*
* COMPUTE GRADE POINT AVERAGE
* _____________________________________________________
* This program accepts as user input from an instructor
* to calculate his/her class's grade point average.
* This will be done through the use of the Do-While
* loop and if-else statments.
* _____________________________________________________
*  INPUT
*      score       : A grade of one of the instructor's students.
*
*  OUTPUT
*      score       : A grade of one of the instructor's students.
*
********************************************************/
int main()
{
/******************************************************
* CONSTANTS
* ____________________________________________________
* A_score          : Variable for a grade of A.
* B_score          : Variable for a grade of B.
* C_score          : Variable for a grade of C.
* D_score          : Variable for a grade of D.
*****************************************************/
const int A_score = 4;
const int B_score = 3;
const int C_score = 2;
const int D_score = 1;
char score;
int count = 1;
int num_of_grades = 0;
int total_gp = 0;
double gpa;
cout << "TEST #" << count << ":nn";
do {
cout << setw(45) << "Enter Letter Grade (enter 'X' to exit): ";
//cin.ignore();
cin >> score;
//cin.get(score);
switch (score)
{
case 'A': num_of_grades += 1;
total_gp += A_score;
break;
case 'a': num_of_grades += 1;
total_gp += A_score;
break;
case 'B': num_of_grades += 1;
total_gp += B_score;
break;
case 'b': num_of_grades += 1;
total_gp += B_score;
break;
case 'C': num_of_grades += 1;
total_gp += C_score;
break;
case 'c': num_of_grades += 1;
total_gp += C_score;
break;
case 'D': num_of_grades += 1;
total_gp += D_score;
break;
case 'd': num_of_grades += 1;
total_gp += D_score;
break;
case 'F': num_of_grades += 1;
total_gp += 0;
break;
case 'f': num_of_grades += 1;
total_gp += 0;
break;
case 'X': gpa = total_gp/num_of_grades;
cout << "nnTotal Grade Points: " << total_gp;
cout << "nGPA: " << gpa << "nn";
count += 1;
cout << "nTEST #" << count << ":nn";
break;
case 'x': gpa = total_gp/num_of_grades;
cout << "nnTotal Grade Points: " << total_gp;
cout << "nGPA: " << setprecision(2) << fixed << gpa << "nn";
count += 1;
cout << "nTEST #" << count << ":nn";
break;
default: cout << "n" << setw(45) << "Invalid letter grade, please try againnn";
}

} while (count < 4);
return 0;
}