How to sort structure data alphabetically?

Question

C++ / C#

Exercise

С клавиатуры ввести последовательность структур, содержащих данные о
результатах сессии студентов группы: <Фамилия, имя>, <Список рейтинговых
оценок>. Распечатать введенные данные в виде таблицы, отсортировав их по
фамилиями студентов в алфавитном порядке. Определить студентов с
самым высоким средним рейтинговым баллом.

My code

#define _CRT_SECURE_NO_WARNINGS
#include<iostream>
#include<string.h>
 
using namespace std;
 
struct Student
{
    char familia[20];
    int exam;
};
void main()
{
    Student sot[128];
    int i, j, a, m;
    char* str;
    cout << "Введите количество студентов: ";
    cin >> a;
    for (i = 0; i < a; i++)
    {
        cout << "\nФамилия " << i + 1 << "-ого студента: ";
        cin >> sot[i].familia;
        cout << "\nРезультаты сессии:  ";
        cin >> sot[i].exam;
    }
 
    for (j = 0; j <= a; j++)
    {
        for (i = 1; i < a; i++)
        {
            if (strcmp(sot[i - 1].familia, sot[i].familia) > 0)
            {
 
                strcpy(str, sot[i - 1].familia);
                strcpy(sot[i - 1].familia, sot[i].familia);
                strcpy(sot[i].familia, str);
            }
        }
    }
    for (i = 0; i < a; i++)
    {
        cout << sot[i].familia << endl;
        cout << sot[i].exam << endl << endl;
    }
}

But, alas, an error occurs: Error C4700 An uninitialized local variable "str" ​​was used.
Tell me how you can fix this problem or show another way to sort structures (qsort, alas, does not work)?

Answer 1

You have a str variable, and as the compiler tells you, you do not initialize it with anything. And below use in . This function takes a pointer to the memory area where the string should be copied. But the pointer points to a random place. Those. the program, even if miraculously compiled, will crash with an exception. You either need to allocate memory for str via malloc, or declare str as a fixed-size char array, like the familia field of a structure. strcpy(str, sot[i - 1].familia)

Answer 2

Use type If you use a pointer, as you are doing now, you need to initialize it, otherwise strcpy will copy it to God knows where (but most likely it will just be segfault)
char str[20];

Answer 3

What does C have to do with it if using namespace std is declared first?
If the standard library is still used, why the hell are these char and dancing with a tambourine?
std::string for strings
std::sort for sorting (adding a string comparison callback) or std::swap if you prefer the cycling algorithm.