Thread: Default Case Keeps Printing In Switch Statement

I'm working on a simple program that maintains parts in a database. The program tracks parts stored in a warehouse. Information about the parts is stored in an array of structures. The program is separated into different operations insert, update, and print.

The program runs fine but for some reason the default case in my switch statement keeps printing out when I try to execute a new code.

Here's what my program inventory.c looks like:

Code:

/* Maintains ia parts database (array version) */
#include <stdio.h>
#include "readline.h"

#define NAME_LEN 25
#define MAX_PARTS 100

struct part{
    int number;
    char name[NAME_LEN + 1];
    int on_hand;
};

int find_part(int number, struct part inv[], int np);
void insert(struct part inv[], int *np);
void search(struct part inv[], int np);
void update(struct part inv[], int np);
void print(struct part inv[], int np);

/********************************************************** 
 * main: Prompts the user to enter an operation code,     * 
 *       then calls a function to perform the requested   * 
 *       action. Repeats until the user enters the        * 
 *       command 'q'. Prints an error message if the user * 
 *       enters an illegal code.                          * 
 **********************************************************/
int main(void){

    char code;
    struct part inventory[MAX_PARTS];
    int num_parts = 0; // number of parts currently stored

    for(;;){
        printf("Enter operation code: ");
        scanf("%c", &code);
        while(getchar() != '\n'); // skips to end of line 
        switch(code){
            case 'i':
                insert(inventory, &num_parts);
                break;
            case 's':
                search(inventory, num_parts);
                break;
            case 'u':
                update(inventory, num_parts);
                break;
            case 'p':
                print(inventory, num_parts);
                break;
            case 'q':
                return 0;
            default:
                printf("Illegal code\n");
        }
        printf("\n");
    }
}

/********************************************************** 
 * find_part: Looks up a part number in the inventory     * 
 *            array. Returns the array index if the part  * 
 *            number is found; otherwise, returns -1.     * 
 **********************************************************/
int find_part(int number, struct part inv[], int np){

    int i;
    for(i = 0; i < np; i++){
        if(inv[i].number == number){
            return i;
        }
    }
    return -1;
}

/********************************************************** 
 * insert: Prompts the user for information about a new   * 
 *         part and then inserts the part into the        * 
 *         database. Prints an error message and returns  * 
 *         prematurely if the part already exists or the  * 
 *         database is full.                              * 
 **********************************************************/
void insert(struct part inv[], int *np){

    int part_number;
    if(*np == MAX_PARTS){
        printf("Database is full; can't add more parts.\n");
        return;
    }
    printf("Enter part number: ");
    scanf("%d", &part_number);
    if(find_part(part_number, inv, *np) >= 0){
        printf("Part already exist\n");
        return;
    }

    inv[*np].number = part_number;
    printf("Enter part name: ");
    read_line(inv[*np].name, NAME_LEN);
    printf("Enter the quantity on hand: ");
    scanf("%d", &inv[*np].on_hand);
    (*np)++;
}

/********************************************************** 
 * search: Prompts the user to enter a part number, then  * 
 *         looks up the part in the database. If the part * 
 *         exists, prints the name and quantity on hand;  * 
 *         if not, prints an error message.               * 
 **********************************************************/
void search(struct part inv[], int np){

    int i, number;

    printf("Enter part number: ");
    scanf("%d", &number);
    i = find_part(number, inv, np);
    if(i >= 0){
        printf("Part name: %s\n", inv[i].name);
        printf("Quantity on hand: %d\n", inv[i].on_hand);
    }
    else{
        printf("Part not found\n");
    }
}

/********************************************************** 
 * update: Prompts the user to enter a part number.       * 
 *         Prints an error message if the part doesn't    * 
 *         exist; otherwise, prompts the user to enter    * 
 *         change in quantity on hand and updates the     * 
 *         database.                                      * 
 **********************************************************/
void update(struct part inv[], int np){

    int i, number, change;
    printf("Enter part number: ");
    scanf("%d", &number);
    i = find_part(number, inv, np);
    if(i >= 0){
        printf("Enter change in quantity on hand: ");
        scanf("%d", &change);
        inv[i].on_hand += change;
    }
    else{
        printf("Part not found\n");
    }
}

/********************************************************** 
 * print: Prints a listing of all parts in the database,  * 
 *        showing the part number, part name, and         * 
 *        quantity on hand. Parts are printed in the      * 
 *        order in which they were entered into the       * 
 *        database.                                       * 
 **********************************************************/
void print(struct part inv[], int np){

    int i;

    printf("Part Number         Part Name                  "
            "Quantity on Hand\n");
    for(i = 0; i < np; i++){
        printf("%7d             %-25s%11d\n", inv[i].number, inv[i].name, inv[i].on_hand);
    }
}

The readline.h header file:

Code:

/*********************************************************
*  From C PROGRAMMING: A MODERN APPROACH, Second Edition *
*  By K. N. King                                         *
*  Copyright (c) 2008, 1996 W. W. Norton & Company, Inc. *
*  All rights reserved.                                  *
*  This program may be freely distributed for class use, *
*  provided that this copyright notice is retained.      *
*********************************************************/
/* readline.h (Chapter 16, page 395) */
#ifndef READLINE_H
#define READLINE_H
/**********************************************************
*  read_line: Skips leading white-space characters, then  *
*  reads the remainder of the input line and   *
*  stores it in str. Truncates the line if its *
*  length exceeds n. Returns the number of     *
*  characters stored.                          *
**********************************************************/
int read_line(char str[], int n);
#endif

The readline.c program:

Code:

/*********************************************************
*  From C PROGRAMMING: A MODERN APPROACH, Second Edition *
*  By K. N. King                                         *
*  Copyright (c) 2008, 1996 W. W. Norton & Company, Inc. *
*  All rights reserved.                                  *
*  This program may be freely distributed for class use, *
*  provided that this copyright notice is retained.      *
*********************************************************/
/* readline.c (Chapter 16, page 395) */

#include <stdio.h>
#include <ctype.h>
#include "readline.h"

int read_line(char str[], int n){

    int ch, i = 0;

    while(isspace(ch = getchar()));
    str[i++] = ch;
    while((ch = getchar()) != '\n'){
        if(i < n){
            str[i++] = ch;
            // ch = getchar();
        }
    }
    str[i] = '\0';
    return i;
}

Here is what my output looks like:


Any input on why my default case keeps printing would be greatly appreciated. Thanks!

Notice that this happens after you ask the user to enter the part number, i.e., you need to do that "skips to end of line" thing after that scanf too.

Originally Posted by laserlight

Notice that this happens after you ask the user to enter the part number, i.e., you need to do that "skips to end of line" thing after that scanf too.

Ah, thanks, now I'm getting the proper output. Do you mind explaining why that kept happening?

The new line character from entering the input was left in the input buffer.

Thank you!