CODEWITHSUNDEEP
cdata-structureslinked-listscanf
user10319858
user10319858

Reputation:

In C,why is my scanf input inside of a linked list node not being taken despite being mentioned in code?

#include <stdio.h>
#include <stdlib.h>
#include <conio.h>
#include <string.h>
#define MAX 30

struct EMP {
    int empno;
    char empName[MAX];
    char designation[MAX];
    struct EMP *next;
};

/*********************************************************************/
/* Function to insert a node at the front of the linked list.        */
/* front: front pointer, id: employee ID, name: employee name        */
/* desg: Employee designation                                        */
/* Returns the new front pointer.                                    */
/*********************************************************************/

struct EMP *insert(struct EMP *front, int id, char name[], char desg[])
{
    struct EMP *newnode;

    newnode = (struct EMP *)malloc(sizeof(struct EMP));

    if (newnode == NULL) {
        printf("\nAllocation failed\n");
        exit(2);
    }
    newnode->empno = id;
    strcpy(newnode->empName, name);
    strcpy(newnode->designation, desg);
    newnode->next = front;
    front = newnode;
    return (front);
}                               /* End of insert() */

/* Function to display a node in a linked list */
void printNode(struct EMP *p)
{
    printf("\nEmployee Details...\n");
    printf("\nEmp No : %d", p->empno);
    printf("\nName : %s", p->empName);
    printf("\nDesignation : %s\n", p->designation);
    printf("-------------------------------------\n");
}                               /* End of printNode() */

/* ******************************************************* */
/* Function to deleteNode a node based on employee number */
/* front: front pointer, id: Key value */
/* Returns: the modified list. */
/* ******************************************************* */

struct EMP *deleteNode(struct EMP *front, int id)
{
    struct EMP *ptr;
    struct EMP *bptr;           /* bptr is pointing to the node behind ptr */

    if (front->empno == id) {
        ptr = front;
        printf("\nNode deleted:");
        printNode(front);
        front = front->next;
        free(ptr);
        return (front);
    }
    for (ptr = front->next, bptr = front; ptr != NULL; ptr = ptr->next, bptr = bptr->next) {
        if (ptr->empno == id) {
            printf("\nNode deleted:");
            printNode(ptr);
            bptr->next = ptr->next;
            free(ptr);
            return (front);
        }
    }
    printf("\nEmployee Number %d not found ", id);
    return (front);
}                               /* End of deleteNode() */

/*****************************************************************/
/* Function to search the nodes in a linear fashion based emp ID */
/* front: front pointer, key: key ID. */
/*****************************************************************/
void search(struct EMP *front, int key)
{
    struct EMP *ptr;

    for (ptr = front; ptr != NULL; ptr = ptr->next) {
        if (ptr->empno == key) {
            printf("\nKey found:");
            printNode(ptr);
            return;
        }
    }
    printf("\nEmployee Number %d not found ", key);
}                               /* End of search() */

/* Function to display the linked list */
void display(struct EMP *front)
{
    struct EMP *ptr;

    for (ptr = front; ptr != NULL; ptr = ptr->next) {
        printNode(ptr);
    }
}                               /* End of display() */

/* Function to display the menu of operations on a linked list */
void menu()
{
    printf("---------------------------------------------\n");
    printf("Press 1 to INSERT a node into the list \n");
    printf("Press 2 to DELETE a node from the list \n");
    printf("Press 3 to DISPLAY the list \n");
    printf("Press 4 to SEARCH the list \n");
    printf("Press 5 to EXIT \n");
    printf("---------------------------------------------\n");
}                               /* End of menu() */

/* Function to select the option */
char option()
{
    char choice;

    printf("\n\n>> Enter your choice: ");
    switch (choice = getche()) {
    case '1':
    case '2':
    case '3':
    case '4':
    case '5':
        return (choice);
    default:
        printf("\nInvalid choice.");
    }
    return choice;
}                               /* End of option() */

/* The main() program begins */
void main()
{
    struct EMP *linkList;
    char name[21], desig[51];
    char choice;
    int eno;

    linkList = NULL;

    printf("\nWelcome to demonstration of singly linked list\n");

    menu();                     /* Function call */

    do {
        choice = option();      /* to choose oeration to be performed */

        switch (choice) {
        case '1':
            printf("\nEnter the Employee Number : ");
            scanf("%d", &eno);

            printf("Enter the Employee name : ");
            fflush(stdin);
            gets(name);

            printf("Enter the Employee Designation : ");
            gets(desig);

            linkList = insert(linkList, eno, name, desig);
            break;

        case '2':
            printf("\n\nEnter the employee number to be deleted: ");
            scanf("%d", &eno);

            linkList = deleteNode(linkList, eno);
            break;

        case '3':
            if (linkList == NULL) {
                printf("\nList empty.");
                break;
            }
            display(linkList);
            break;

        case '4':
            printf("\n\nEnter the employee number to be searched: ");
            scanf("%d", &eno);

            search(linkList, eno);
            break;

        case '5':
            break;
        }
    } while (choice != '5');
}                               /* End of main() */

However , when I run the program , the program is not accepting the value for Employee name and directly jumping to Employee designation .

As you can see in the screenshot of the output linked, it is directly jumping to the employee designation without taking input for employee name

Why is this happening ?

Edit 1: I was told to try replacing 'gets' with 'fgets' . Despite doing that , the computer is still now taking the input for employee name and directly jumping to employee designation

  #include <stdio.h>
#include <stdlib.h>
#include <conio.h>
#include <string.h>
#define MAX 30

struct EMP
{
int empno;
char empName[MAX];
char designation[MAX];
struct EMP *next;
};

/*********************************************************************/
/* Function to insert a node at the front of the linked list. */
/* front: front pointer, id: employee ID, name: employee name */
/* desg: Employee designation */
/* Returns the new front pointer. */
/*********************************************************************/

struct EMP* insert(struct EMP *front, int id, char name[], char desg[])
{
struct EMP *newnode;

newnode = (struct EMP*) malloc(sizeof(struct EMP));

if (newnode == NULL)
{
printf("\nAllocation failed\n");
exit(2);
}
newnode->empno = id;
strcpy(newnode->empName, name);
strcpy(newnode->designation, desg);
newnode->next = front;
front = newnode;
return(front);
} /*End of insert() */

/* Function to display a node in a linked list */
void printNode(struct EMP *p)
{
printf("\nEmployee Details...\n");
printf("\nEmp No : %d", p->empno);
printf("\nName : %s", p->empName);
printf("\nDesignation : %s\n", p->designation);
printf("-------------------------------------\n");
} /*End of printNode() */

/* ********************************************************/
/* Function to deleteNode a node based on employee number */
/* front: front pointer, id: Key value */
/* Returns: the modified list. */
/* ********************************************************/

struct EMP* deleteNode(struct EMP *front, int id)
{
struct EMP *ptr;
struct EMP *bptr; /* bptr is pointing to the node behind ptr */

if (front->empno == id)
{
ptr = front;
printf("\nNode deleted:");
printNode(front);
front = front->next;
free(ptr);
return(front);
}

for(ptr=front->next, bptr=front; ptr!=NULL; ptr=ptr->next, bptr=bptr->next)
{
if (ptr->empno == id)
{
printf("\nNode deleted:");
printNode(ptr);
bptr->next = ptr->next;
free(ptr);
return(front);
}
}
printf("\nEmployee Number %d not found ", id);
return(front);
} /*End of deleteNode() */

/*****************************************************************/
/* Function to search the nodes in a linear fashion based emp ID */
/* front: front pointer, key: key ID. */
/*****************************************************************/
void search(struct EMP *front, int key)
{
struct EMP *ptr;

for (ptr = front; ptr != NULL; ptr = ptr -> next)
{
if (ptr->empno == key)
{
printf("\nKey found:");
printNode(ptr);
return;
}
}
printf("\nEmployee Number %d not found ", key);
} /*End of search() */

/* Function to display the linked list */
void display(struct EMP *front)
{
struct EMP *ptr;

for (ptr = front; ptr != NULL; ptr = ptr->next)
{
printNode(ptr);
}
} /*End of display() */

/* Function to display the menu of operations on a linked list */
void menu()
{
printf("---------------------------------------------\n");
printf("Press 1 to INSERT a node into the list \n");
printf("Press 2 to DELETE a node from the list \n");
printf("Press 3 to DISPLAY the list \n");
printf("Press 4 to SEARCH the list \n");
printf("Press 5 to EXIT \n");
printf("---------------------------------------------\n");
} /*End of menu() */

/* Function to select the option */
char option()
{
char choice;

printf("\n\n>> Enter your choice: ");
switch(choice=getche())
{
case '1':
case '2':
case '3':
case '4':
case '5': return(choice);
default : printf("\nInvalid choice.");
}
return choice;
} /*End of option() */

/* The main() program begins */
void main()
{
struct EMP *linkList;
char name[21], desig[51];
char choice;
int eno;

linkList = NULL;

printf("\nWelcome to demonstration of singly linked list\n");

menu(); /*Function call */

do {
choice = option(); /*to choose oeration to be performed */

switch(choice)
{
case '1':

printf("\nEnter the Employee Number : ");
scanf("%d", &eno);

printf("Enter the Employee name : ");
    //fflush(stdin);
    fgets(name,MAX,stdin);


printf("Enter the Employee Designation : ");
fgets(desig,MAX,stdin);

linkList = insert(linkList, eno, name, desig);
break;

case '2': printf("\n\nEnter the employee number to be deleted: ");
scanf("%d", &eno);

linkList = deleteNode(linkList, eno);
break;

case '3': if (linkList == NULL)
{
printf("\nList empty.");
break;
}
display(linkList);
break;

case '4': printf("\n\nEnter the employee number to be searched: ");
scanf("%d", &eno);

search(linkList, eno);
break;

case '5': break;
}
} while (choice != '5');
} /*End fo main()*/

Upvotes: 0

Views: 722

Answers (2)

nullp0tr
nullp0tr

Reputation: 485

Answer to the question in the title

Input is not taken because you're mixing the scanf and gets family of functions. scanf leaves the new line character in the buffer, and then when you call fgets to acquire the new line, but fgets finds a new line as the first character and returns immediately.

Suggestion

Pick only one of the *get* and *scanf* families to handle your input. You can still use fgets to get the input, and then pass it to sscanf, to handle the format and retrieve your values.

Example

do {
    choice = option();      /* to choose oeration to be performed */

    char line_buffer[128];  // Declare your own line buffer
    setbuf(stdin, NULL);  // Set stdin to unbuffered

    switch (choice) {
    case '1':
        printf("\nEnter the Employee Number : ");
        // put input into line buffer
        fgets(line_buffer, sizeof(line_buffer), stdin); 
        // use sscanf on your line_buffer instead of stdin
        sscanf(line_buffer, "%d", &eno); 

        printf("Enter the Employee name : ");
        fgets(name, sizeof(name), stdin);

        printf("Enter the Employee Designation : ");
        fgets(desig, sizeof(desig), stdin);

        linkList = insert(linkList, eno, name, desig);
        break;
// ...

Upvotes: 1

restless_soul469
restless_soul469

Reputation: 137

The problem here is \n is in buffer stdin when you are taking input using gets(). gets() reads stdin(if no buffer is specified) buffer till \n.

One naive solution would be read an extra character that that will eat up \n. The idea is you can use any of the following just after using scanf() to consume \n from the buffer,

  1. gets();
  2. getc(stdin);
  3. getchar();

Upvotes: 0

Related Questions