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  • printing reverse in singly link list using pointers

    - by theoneabhinav
    i have been trying this code. i think the logic is ok but the program terminates abruptly when the display_rev function is called here is code of display_rev void display_rev(emp_node *head) { emp_node *p=head, *q; while(p->next != NULL) p=p->next; while(p!=head || p==head){ q=head; display_rec(p); while(q->next != p) q=q->next; p=q; } } here is my whole code #include<stdio.h> #include<stdlib.h> #include<ctype.h> #include<string.h> //Declarations=============================================================== typedef struct //employee record { int emp_id; char name[150]; char mob_no[11]; float salary; int proj[5]; struct emp_node *next; } emp_node; emp_node* add_rec(emp_node*); emp_node* create_db(emp_node*); emp_node* search_db(emp_node*, int); emp_node* delete_rec(emp_node*, int); void read_name(emp_node*); void read_mob(emp_node*); void display_db(emp_node*); void display_rec(emp_node*); void display_rev(emp_node*); void modify_rec(emp_node*); void swtch(emp_node*); //=========================================================================== int main() { char ans; emp_node *head = NULL; head = create_db(head); display_db(head); do { swtch(head); printf("\n\n\tDo you want to continue (y/n) : "); getchar(); scanf("%c", &ans); } while (ans == 'y' || ans == 'Y'); return 0; } //Definitions================================================================ emp_node* create_db(emp_node *head) //database creation { int i = 1, no; emp_node *p; printf("Enter number of employees:"); scanf("%d", &no); printf("\n\n"); head = (emp_node *) malloc(sizeof(emp_node)); head = add_rec(head); head->next = NULL; p = head; while (i < no) { p->next = (emp_node *) malloc(sizeof(emp_node)); p = p->next; p = add_rec(p); p->next = NULL; i++; } return head; } emp_node* add_rec(emp_node *p) //new record { int j; printf("\n\tEmployee ID : "); scanf("%d", &(p->emp_id)); printf("\n\tFirst Name:"); read_name(p); printf("\n\tMobile No.:"); read_mob(p); printf("\n\tSalary :"); scanf("%f", &(p->salary)); printf( "\n\tEnter \"1\" for the projects employee is working on, otherwise enter \"0\": \n"); for (j = 0; j < 5; j++) { printf("\n\t\tProject No. %d : ", j + 1); scanf("%d", &(p->proj[j])); while (p->proj[j] != 1 && p->proj[j] != 0) { printf("\n\nInvalid entry!! Please re-enter."); printf("\n\t\tProject No. %d : ", j + 1); scanf("%d", &(p->proj[j])); } } printf("\n\n\n"); return p; } void read_name(emp_node *p) //validation for name { int j, len; scanf("%s", p->name); len = strlen(p->name); for (j = 0; j < len; j++) { if (!isalpha(p->name[j])) { printf( "\n\n\tInvalid name!!Can contain only characters. Please Re-enter.\n"); printf("\n\tName : "); read_name(p); } } } void read_mob(emp_node *p) //validation for mobile no. { int j; scanf("%s", p->mob_no); while (strlen(p->mob_no) != 10) { printf("\n\nInvalid Mobile No!!Please Re-enter"); printf("\n\n\tMobile No.:"); read_mob(p); } for (j = 0; j < 10; j++) { if (!(48 <= p->mob_no[j] && p->mob_no[j] <= 57)) { printf( "\n\nInvalid Mobile No!!Can contain only digits. Please Re-enter."); printf("\n\n\tMobile No.:"); read_mob(p); } } } void display_db(emp_node *head) //displaying whole database { emp_node *p; p = head; printf("\n\n\t\t****** EMPLOYEE DATABASE ******\n"); printf( "\n=============================================================================="); printf("\n Id.\t Name\t\t Mobile No\t Salary\t Projects\n"); while (p != NULL) { display_rec(p); p = p->next; printf("\n\n\n"); } printf( "\n=============================================================================="); } void swtch(emp_node *head) //function for menu and switch case { int cho, x; emp_node *p; printf("\n\n\t\t****** MENU ******"); printf( "\n\n\t1. insert Record\n\t2. Search Record\n\t3. Modify Record\n\t4. Delete Record\n\t5. Display Reverse\n\t6. Exit"); printf("\n\tWhich operation do you want to perform? "); scanf("%d", &cho); switch (cho) { case 1: p=head; while(p->next != NULL) p=p->next; p->next = (emp_node *) malloc(sizeof(emp_node)); p=p->next; p = add_rec(p); p->next = NULL; display_db(head); break; case 2: printf("\n\n\tEnter employee ID whose record is to be Searched :"); scanf("%d", &x); p = search_db(head, x); if (p == NULL) printf("\n\nRecord not found."); else display_rec(p); break; case 3: printf("\n\n\tEnter employee ID whose record is to be modified :"); scanf("%d", &x); p = search_db(head, x); if (p == NULL) printf("\n\nRecord not found."); else modify_rec(p); display_db(head); break; case 4: printf("\n\n\tEnter employee ID whose record is to be deleted :"); scanf("%d", &x); head = delete_rec(head, x); display_db(head); break; case 5: display_rev(head); case 6: exit(0); default: printf("Invalid Choice!! Please try again."); } } emp_node* search_db(emp_node *head, int id) //search database { emp_node *p = head; while (p != NULL) { if (p->emp_id == id) return p; p = p->next; } return NULL; } void display_rec(emp_node *p) //display a single record { int j; printf("\n %d", p->emp_id); printf("\t %10s", p->name); printf("\t %10s", p->mob_no); printf("\t %05.2f", p->salary); printf("\t "); for (j = 0; j < 5; j++) { if (p->proj[j] == 1) printf(" %d,", j + 1); } } void modify_rec(emp_node *p) //modifying a record { int j, cho; char ch1, edt; do { printf( "\n\t1. Name\n\t2. Email Address\n\t3. Mobile No.\n\t4. Salary\n\t5. Date of birth\n\t6. Projects\n"); printf("Enter your choice : "); scanf("%d", &cho); switch (cho) { case 1: printf("\n\tPrevious name:%s", p->name); printf("\n\tDo you want to edit ? (y/n)"); getchar(); scanf("%c", &ch1); if (ch1 == 'y' || ch1 == 'Y') { printf("\n\tEnter New Name:"); read_name(p); } break; case 2: printf("\n\tPrevious Mobile No. : %s", p->mob_no); printf("\n\tDo you want to edit ? (y/n)"); getchar(); scanf("%c", &ch1); if (ch1 == 'y' || ch1 == 'Y') { printf("\n\tEnter New Mobile No. :"); read_mob(p); } break; case 3: printf("\n\tPrevious salary is : %f", p->salary); printf("\n\tDo you want to edit ? (y/n)"); getchar(); scanf("%c", &ch1); if (ch1 == 'y' || ch1 == 'Y') { printf("\n\tEnter New salary:"); scanf("%f", &(p->salary)); } break; case 4: printf("the employee is currently working on project no. "); for (j = 0; j < 5; j++) { if (p->proj[j] == 1) printf(" %d,", j + 1); } printf("\n\tDo you want to edit ? (y/n)"); getchar(); scanf("%c", &ch1); if (ch1 == 'y' || ch1 == 'Y') { printf( "\n\tEnter \"1\" for the projects employee is working on : \n"); for (j = 0; j < 5; j++) { printf("\n\t\tProject No. %d : ", j + 1); scanf("%d", &(p->proj[j])); while (p->proj[j] != 1) { printf("\n\nInvalid entry!! Please re-enter."); printf("\n\t\tProject No. %d : ", j + 1); scanf("%d", &(p->proj[j])); } } } break; default: printf("\n\nInvalid Choice!! Please Try again."); } printf("\n\nDo you want to edit any other fields ?(y/n)"); getchar(); scanf("%c", &edt); } while (edt == 'y' || edt == 'Y'); } emp_node* delete_rec(emp_node *head, int id) //physical deletion of record { emp_node *p = head, *q; if (head->emp_id == id) { head = head->next; free(p); return head; } else { q = p->next; while (q->emp_id != id) { p = p->next; q = q->next; } if (q->next == NULL) p->next = NULL; else p->next = q->next; free(q); return head; } } void display_rev(emp_node *head) { emp_node *p=head, *q; while(p->next != NULL) p=p->next; while(p!=head || p==head){ q=head; display_rec(p); while(q->next != p) q=q->next; p=q; } }

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