Count and modify the elements of a queue

This is the code in the C++ language that I prepared and that does what you request in your question: Count the elements of the list, and be able to access the elements to modify them, either by your index or by looking for a character.

Code:

#include <iostream>

typedef struct node {
    char data;
    struct node *next;
} node_t;

void print_list(node_t *);
void count_list_elements(node_t *);
void modify_an_item_by_index(node_t *, int, char);
void modify_an_item_by_char(node_t *head, char i, char new_data);

int main(void) {
    int i;
    char u;
    char data;

    node_t *head = NULL;
    head = new node_t();

    head->data = 'a';
    head->next = new node_t();
    head->next->data = 'e';
    head->next->next = NULL;
    std::cout << "List: " << std::endl;
    print_list(head);
    std::cout << "Ingresa el indice del elemento a modificar (comienza desde 0): ";
    std::cin >> i;
    std::cout << "Ingresa el nuevo valor: ";
    std::cin >> data;
    modify_an_item_by_index(head, i, data);
    std::cout << "Ingresa el caracter a buscar: ";
    std::cin >> u;
    std::cout << "Ingresa el nuevo valor: ";
    std::cin >> data;
    modify_an_item_by_char(head, u, data);
    print_list(head);
    count_list_elements(head);

    return 0;
}

void print_list(node_t *head) {
    node_t *current = head;

    while (current != NULL) {
        std::cout << current->data << std::endl;
        current = current->next;
    }
}

void count_list_elements(node_t *head) {
    node_t *current = head;
    int n = 0;

    while (current != NULL) {
        current = current->next;
        n += 1;
    }

    std::cout << "La lista tiene " << n << " elementos." << std::endl;
}

void modify_an_item_by_index(node_t *head, int i, char new_data) {
    node_t *current = head;

    for(int x = 0; x < i; x++) {
        current = current->next;
    }

    current->data = new_data;
}

void modify_an_item_by_char(node_t *head, char i, char new_data) {
    node_t *current = head;

    while (current != NULL) {
        if (current->data == i) {
            break;
        }
        current = current->next;
    }

    current->data = new_data;
}

Brief explanation: Observe how the functions that are responsible for modifying the values of a nodo first create a pointer to node called current and is a copy of the pointer to node head , is done in this way so as not to lose your head from the list head , and with current you can browse through the nodes until you find the node with the indicated index or character (depends on which of the two functions you use). Once the node is identified, we can access its values and modify them with the desired value.

As for counting the nodes, we have something very similar to the previous one but much simpler since you only need to go through the list of nodes through the pointer to node current (which is a copy of head ) and store the iterations within a variable and then display it on the screen.

When executing the program and passing some parameters, the following output / result is obtained:

List:
a
e
Ingresa el indice del elemento a modificar (comienza desde 0): 0
Ingresa el nuevo valor: o
Ingresa el caracter a buscar: e
Ingresa el nuevo valor: u
o
u
La lista tiene 2 elementos.

Note: Validations to avoid inappropriate behavior are all yours. I did not include them because it could complicate the understanding of the answer to your question.

Since you have labeled the question as C ++, you should use the language correctly:

• The header <stdlib.h> is from c not from