How to insert a new node to the sorted linked list in C?

Question

SortByNum and SortByName functions are working but the inserting is not.

Is there other ways to do it and why it is not working can someone explain it?

Here is the code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

struct studInfo {
    int studNr;
    char studName[12];
    int grade;
};

struct node {
    struct studInfo info;
    struct node *link;
};

typedef struct node *NODEPTR;

NODEPTR getnode(void);
void fileIntoArray(struct studInfo allStudent[], int *num);
void sortByNum(struct studInfo allstudent[], NODEPTR *, int num);
void sortByName(struct studInfo allstudent[], NODEPTR *, int num);
void insert(NODEPTR *, NODEPTR *, NODEPTR);
void list(NODEPTR);

int main() {
    struct studInfo allStudent[150];
    NODEPTR headNum, headName, m;
    int choice;
    int num;

    fileIntoArray(allStudent, &num);
    sortByNum(allStudent, &headNum, num);
    // sortByName(allStudent, &headName, num);
    // list(headName);
    m = getnode();
    printf("Enter a sudent infomation STUDENT Num, Name, Grade");
    scanf("%d", &m->info.studNr);
    scanf("%s", m->info.studName);
    scanf("%d", &m->info.grade);
    insert(&headNum, &headName, m);
    list(headNum);

    return 0;
}

void fileIntoArray(struct studInfo allStudent[], int *num) {
    FILE *ptr = fopen("student.txt", "r");
    int i = 0;
    while (!feof(ptr)) {
        fscanf(ptr, "%d%s%d", &allStudent[i].studNr,
               allStudent[i].studName, &allStudent[i].grade);
        i++;
    }
    *num = i;
    fclose(ptr);
}

void sortByNum(struct studInfo allStudent[], NODEPTR *headNum, int num) {
    NODEPTR head, p, prev;
    head = NULL;
    p = NULL;
    prev = NULL;
    for (int i = 0; i < num; i++) {
        p = getnode();
        p->info = allStudent[i];
        if (head == NULL || p->info.studNr < head->info.studNr) {
            p->link = head;
            head = p;
        } else {
            prev = head;
            while (prev->link && prev->link->info.studNr < p->info.studNr) {
                prev = prev->link;
            }
            p->link = prev->link;
            prev->link = p;
        }
    }
    *headNum = head;
}

void sortByName(struct studInfo allStudent[], NODEPTR *headName, int num) {
    NODEPTR head,p,prev;
    head = NULL;
    for (int i = 0; i < num; ++i) {
        p = getnode();
        p->info = allStudent[i];
        if (head == NULL || strcmp(p->info.studName, head->info.studName) < 0) {
            p->link = head;
            head = p;
        } else {
            prev = head;
            while (prev->link && strcmp(prev->link->info.studName, p->info.studName) < 0) {
                prev = prev->link;
            }
            p->link = prev->link;
            prev->link = p;
        }
    }
    *headName = head;
}

void insert(NODEPTR *headNum, NODEPTR *headName, NODEPTR p) {
    NODEPTR head;
    int key = p->info.studNr;

    while ((*headNum)->link != NULL && (*headNum)->link->info.studNr < key) {
        p->link = (*headNum)->link;
        (*headNum)->link = p;
    }
}

void list(NODEPTR p) {
    int line = 0, c;
    while (p != NULL) {
        line++;
        if (line > 25) {
            printf("Press enter>");
            fflush(stdout);
            while ((c = getchar()) != EOF && c != '\n')
                continue;
            printf("\r            \r");
            line = 1;
        }
        printf("%d %d  %s  %d\n", line, p->info.studNr,
               p->info.studName, p->info.grade);
        p = p->link;
    }
}

NODEPTR getnode(void) {
    NODEPTR q;
    q = (NODEPTR)malloc(sizeof(struct node));
    return (q);
}

Have you tried running your code line by line in a debugger while monitoring the values of all variables, in order to determine in which line your program stops behaving as intended? If you did not try this, then you may want to read this: [What is a debugger and how can it help me diagnose problems?](https://stackoverflow.com/q/25385173/12149471) You may also want to read this: [How to debug small programs?](https://ericlippert.com/2014/03/05/how-to-debug-small-programs/) — Andreas Wenzel, May 29 '22 at 13:59
SO questions need to be self-contained. In particular, whatever code you're asking about needs to appear in the question itself, as code-formatted text. But not the full program: we're looking for a [mre] that demonstrates the problem. — John Bollinger, May 29 '22 at 14:00
Off the top of my head, however, it is suspicious that you ask about inserting into a sorted linked list, but also describe two distinct sort orders. If you're trying to insert in a way that keeps the list sorted, then the insert needs to take the current order into account. If not, then the "sorted" part is irrelevant. — John Bollinger, May 29 '22 at 14:03
You cannot insert the same node into 2 different lists. You should pass the address of the student struct and let `insert` insert a new node into each of the lists. — chqrlie, May 29 '22 at 14:11

How to insert a new node to the sorted linked list in C?

0 Answers0