C++ how to pass string array in function and assign to a variable?

You can not assign array of strings string a[] to array courseTaken using = operator. The expression string a[] is equivalent to std::string*. That is why you get the compiler error.

This may be what you wanted:

#include <iostream>
using namespace std;

class Student
{
    public:
        string studentName;
        string courseTaken[3];
        void setStudent(string n, string a[]); 
};

void setStudent(string n, string a[]); 

void Student::setStudent(string n, string a[])
{
   studentName = n;
   for(int i=0; i < sizeof(courseTaken)/sizeof(courseTaken[0]); i++)
    courseTaken[i] = a[i];
}

int main()
{
    Student student;

    string courses[3] = {"Cobol","C++","Fortran"};
    student.setStudent("Eva", courses);

    for (int i = 0; i < 3; i++){
        cout << student.courseTaken[i] << endl;
    }

    return 0;
}

Output:

Cobol                                                                                                                                        
C++                                                                                                                                          
Fortran 

It seems you don't understand array decay mechanism of C-format arrays. For many context, an array name will be explained as a pointer to the first element of the array. And this pointer is a prvalue which just like this pointer, you can NOT assign to it. the "modern Cpp way"(C++11) is to use std::array, which overloaded the =operator and stores the size of the array so that it won't be decayed while passing to a function. The second way is to pass the reference, with a template you can ensure the array's size, then use std::memcpy. And you can add a parameter stores the array's size, and then you can use memcpy too. I hope you use the first way, don't forget -std=c++11

This is because you are passing an array to a variable that's why this error occurs. To solve this problem you may use pointer in argument to solve this problem. Change your function to this.

void Student::setStudent(string n, string* a)
{
   studentName= n;
   courseTaken = a;
}