Dynamic allocation for structure array in C database

Question

I am trying to create a database in C. It has to have 3 functions: add new data, delete data and sort the data. I want the program to read the data and store it in an array of structures, so I can easily work with it later.

typedef struct Customer
{
    char name[20];
    char surname[20];
    char destination[30];
}customer;
customer *ptr;

int n, i, delete, switch;
char buffer[1024], *sp;

At the start, the program reads the data from the csv file, allocates memory and assigns the data to an array of structures.

int main()
{
    n = countRows();
    ptr = (customer*)malloc(n*sizeof(customer));
    assignData();

Next using a switch statement, the user chooses what to do:

while(true)
    {
        printf("1) Print data.\n");
        printf("2) Data entry.\n");
        printf("3) Remove data.\n");
        printf("0) Close the program.\n");
        printf("Choose action: ");
        scanf("%d",&vyber);

switch(switch)
    {

    case 1:
        system("cls");
        printData();
        break;

    case 2:
        system("cls");
        addData();
        break;

    case 3:
        system("cls");
        printData();
        printf("Enter number of row to remove: ");
        scanf("%d",&delete);
        removeData(delete);
        break;

    case 0:
        exit(0);
    }
    }
    return 0;
    free(ptr);
}

These are my functions:

int countRows()
{
    FILE *fr = fopen("data.csv","r+");

        n=0;
    while(fgets(buffer,1024,fr)!=NULL)
        n++;

    rewind(fr);
    fclose(fr);
    return n;
}

void assignData()
{
    n = countRows();
    ptr = (customer*)realloc(ptr,n*sizeof(customer));

    FILE *fp = fopen("data.csv","r");

    while(fgets(buffer,1024,fp)!=NULL)
    {
        sp = strtok(buffer, ";");
        strcpy(ptr[i].name,sp);

        sp = strtok(NULL, ";");
        strcpy(ptr[i].surname,sp);

        sp = strtok(NULL, ";");
        strcpy(ptr[i].destination,sp);

        i++;
    }
    rewind(fp);
    fclose(fp);
}

void addData()
{
    FILE *fa = fopen("data.csv","a");

    char fna[20], sna[20], des[30];
            printf("\n");
            printf("First name: ");
            fflush(stdin);
            gets(fna);
            printf("Surname: ");
            fflush(stdin);
            gets(sna);
            printf("Destination: ");
            fflush(stdin);
            gets(des);
    fprintf(fa,"%s;%s;%s\n",fna,sna,des);


    n = countRows();
    ptr = (customer*)realloc(ptr,n*sizeof(customer));


            strcpy(ptr[n].name,fna);
            strcpy(ptr[n].surname,sna);
            strcpy(ptr[n].destination,des);

    rewind(fa);
    fclose(fa);
}
 
void printData()
{
    n = countRows();
    for(int x = 0; x<n;x++)
        printf("%d %20s %20s %20s\n",x,ptr[x].name,ptr[x].surname,ptr[x].destination);
}

void removeData(remove)
{
    n = countRows();

    FILE *fd = fopen("data.csv","w");

    for(int m=0;m<n;m++)
    {
        if(remove!=m)
            fprintf(fd,"%s;%s;%s",ptr[m].name,ptr[m].surname,ptr[m].destination);
    }
    rewind(fd);
    fclose(fd);
}

I am having issues mainly with the addData function. It works, but there is a limited amount of data entries I can have before the program crashes (1 or 2). I suspect the problem is that I am not allocating memory correctly.