我在交换病人姓名的“ trier”功能中做的错误吗？

Question

The exercise about creating a linked list for patient, then arrange it by their name. I'm trying to swap their name; it seems that what I did doesn't work.

I've tried to take the the previous pointer "prec" and compare the name of next pointer "ptr" then I tried to swap their name in function named "echangedeChaine"

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

struct patient{
    int cin;
    char nom[8];
    char prenom[8];
    int annee;
    struct patient *suivant;
};

struct patient *tete=NULL;

void creationdePatient(){
    struct patient* ptr;
    char rep;

    ptr = malloc(sizeof(struct patient));
    tete =ptr;
    printf("Saisir Numero de Cin de Nouveau Patient: ");
    scanf("%d",&tete->cin);
    printf("Saisir Nom de Patient: ");
    scanf("%8s",&tete->nom);
    printf("Saisir prenom de Patient: ");
    scanf("%8s",&tete->prenom);
    tete->suivant = NULL;
    printf("\nVoulez vous Saisir un autre Patient ?: (O,N): \n");
    scanf(" %c",&rep);

    while(toupper(rep)=='O'){
        ptr = malloc(sizeof(struct patient));
        printf("Saisir Numero de Cin de Nouveau Patient: ");
        scanf("%d",&ptr->cin);
        printf("Saisir Nom de Patient: ");
        scanf("%8s",&ptr->nom);
        printf("Saisir prenom de Patient: ");
        scanf("%8s",&ptr->prenom);
        ptr->suivant = tete;
        tete=ptr;
        printf("\nVoulez vous Saisir un autre Patient ?: (O,N): \n");
        scanf(" %c",&rep);
    }
}

void echangedeChaine(char x[8] , char y[8]){
    char temp[8];
    strcpy(temp,y);
    strcpy(y,x);
    strcpy(x,temp);
}


void printtList(){
    struct patient *temp = tete;

    while(temp!=NULL){
        printf("Cin: %d | Nom:%s | Prenom: %s\n", temp->cin, temp->nom, temp->prenom);
        temp=temp->suivant;
    }
}


void trier(){
    struct patient *ptr = tete;
    struct patient*prec;
    int echange=0;
    do{
        while(ptr!=NULL){
            prec=ptr;
            ptr=ptr->suivant;
            if(strcmp(prec->nom,ptr->nom)<0){
                echangedeChaine(prec->nom,ptr->nom);
                echange=1;
            }
        }
    }while(echange==1);
}

int main()
{
   creationdePatient();
   printtList();
   trier();
   printtList();
}

It seems it doesn't work after I tried to execute it.

Answer 1

The are several issues with your code, including (but not necessarily limited to):

1. Your code in trier() will dereference a NULL pointer at the last element - since its suivant is NULL, and you're doing:

    ptr = ptr->suivant; if(strcmp(prec->nom,ptr->nom) < 0) { ... } 

2. I think you're trying to sort in the wrong order: When strcmp(prec->nom,ptr->nom) is negative, that means the first patient's name is lexicographically earlier than the following patient name - in which case they should not be exchanged.

---

PS - for those not fluent in French, here's a little glossary for OP's program...

tete = head
suivant = next
nom = last/family name
prenom = first/given name
echange = change (or replace)
chaine = list (or cain)