A contact database using a dynamic-single linked list in ANSI C

/*Contact Management Database using a dynamic - single linked list
Author : P J Wells
Compiled on Dev-C++, Bloodshed Software.
Date : 03/04/08
*/

/*----------------------------------------------------------------------------*/
/* Define libraries to be included */
#include <stdio.h>
#include <malloc.h>
#include <string.h>
#include <ctype.h>
/*----------------------------------------------------------------------------*/
/* Define Functions*/
void clearInput(void);
void addNewcontact(void);
void listAll(void);
void deletecontact(void);
void modifycontact(void);
int findcontact(void);
int prompt(void);
int findnum (int);

/*----------------------------------------------------------------------------*/
/* Define Structures*/

typedef struct contact {   
    int number;        /*unique account number*/
    char name[20];     /*contains name*/  
    char phone[15];    /*contains phone number*/
    char email[20];           /*contains email address*/
    struct contact *next; /*next is used to navigate through structures.*/ 
    int count;     /*count is used to input comments into array*/    
    } Contact;
Contact *firstc,*currentc,*newc; /*pointers*/
/* firstc is used to point to first record in list
currentc points to current record in list
newc contains address of new structure/node 
*/
int cnum = 0; /*gives unique account numbers*/


/*----------------------------------------------------------------------------*/
/* Main Function */

int main()
{
    FILE *datafile;
    char *filename = "contactdatabase.dat";/*declare file name*/
    char ch;
    firstc = NULL;

    datafile = fopen(filename,"r");/* open file for reading*/
    
    if(datafile)	 
    {
	    firstc = (struct contact *)malloc(sizeof(struct contact));
    /*use of malloc to set aside memory relative to size of structure contact*/
	    currentc = firstc;       /*make first record current*/
	    while(1) /*endless while loop. a NULL pointer in final node ends loop*/
     	    {
		    newc = (struct contact *)malloc(sizeof(struct contact));
		    fread(currentc,sizeof(struct contact),1,datafile);
		    if(currentc->next == NULL)   /* NULL indicates end of node list*/
			    break;
		    currentc->next = newc;       /* pointer referencing next node*/
            currentc->count=0;           /* initiates count for comments*/
		    currentc = newc;             /* make current record new*/
	    }
	    fclose(datafile);                /* close file - good practice to cloe files after use*/
	    cnum = currentc->number;         
        
    }
        
    do
    {
	fflush(stdin);
        puts("\nWelcome To The Contact Database");/* print menu messages*/
        puts("-- -----------------------------");
        puts("1 - Add a new contact");     
	puts("2 - Delete contact");          
	puts("3 - List all contacts");       
	puts("4 - Modify contact");          
	puts("5 - Find a contact by name");  
	puts("-- -----------------------------");
        puts("Q - Save and quit\n");         
        printf("\tYour choice:");            
        ch = getchar();
	    ch = toupper(ch);/*changes user input case to upper case*/
        switch(ch)     /*stores in ch variable.*/
        {
            case '1':
                puts("Add a new contact\n");
	        fflush(stdin);
                addNewcontact();//call addNewcontact function 
                break;
	    case '2':
		puts("Delete a contact\n");
		deletecontact();
		break;
	    case '3':
		puts("List all contacts\n");
		listAll();
		break;
	    case '4':
		puts("Modify a contact\n");
		modifycontact();
		break;
	    case '5':
		puts("Find a contact by name\n");
		findcontact();
		break;
            case 'Q':
                puts("Save and quit\n");
                default:
                break;
        }
    }
    while(ch != 'Q');

/*
 * Save the records to disk
 */
    currentc = firstc;
    
    if(currentc == NULL)
	    return(0);		/*no data to write*/
				  
    datafile = fopen(filename,"w");   /*open file to write*/
    
    if(datafile == NULL)
    {
	    printf("Error writing to %s\n",filename);
	    return(1);
    }
    				/* Write each record to disk*/ 
    while(currentc != NULL)
    {
	    fwrite(currentc,sizeof(struct contact),1,datafile);
	    currentc = currentc->next;
    }
    fclose(datafile);             /*closes data file*/
    return(0);
}
/*----------------------------------------------------------------------------*/
void addNewcontact(void) /* add new contact function*/
{
    newc = (struct contact *)malloc(sizeof(struct contact)); 
    /*allocates memory for new structure.*/

/*
 * Checks to see whether this is the first record in file
 * If so, then all pointers are initialized to this record,
 */

    if(firstc==NULL)
        firstc = currentc = newc;

/* 
 * if not, end of structure list is obtained
 */

    else
    {
        currentc = firstc;      /* make the first record the current one*/ 
                                

        while(currentc->next != NULL)currentc = currentc->next;
                                /* and loop through all records*/ 
        currentc->next = newc;  /* pointer to next node */
        currentc = newc;        /* make current record the new one*/ 
    }

/* update the structure */

    cnum++;
    printf("%27s: %5i\n","contact number",cnum);
    currentc->number = cnum;    /*cnum is used to give unique account numbers*/
    
    printf("%27s: ","Enter contact name");
    gets(currentc->name);

    printf("%27s: ","Enter contact Phone number");
    gets(currentc->phone);

    printf("%27s: ","Enter contact email");
    gets(currentc->email);
    printf("contact added!");
    currentc->count=0;

/* 
 * gives the new record a NULL pointer
 * to show it's the last record:
 */

    currentc->next = NULL;
}
/*----------------------------------------------------------------------------*/
void listAll(void) /* list all contacts function*/
{
    if(firstc==NULL)
        puts("There are no contacts to display!"); /*prints message*/
        
    else
    {
	    printf("%6s %-20s %-15s %-15s\n","Acct#","Name","Phone","Email");
        puts("------ -------------------- ------------- -------------------");           
                            /*prints table titles*/
        currentc=firstc;
        
        do
        {
        
                printf("%6d: %-20s %-15s %-20s\n",\
                currentc->number,\
                currentc->name,\
                currentc->phone,\
                currentc->email); 
                /*prints values of number, name, phone and email*/
        }
        
        while((currentc=currentc->next) != NULL);
    }
}
/*----------------------------------------------------------------------------*/
void deletecontact(void)     /*delete contact function */          
{
    int record;
    struct contact *previousa;

    if(firstc==NULL)
    {
        puts("There are no contacts to delete!");
	return;
    }
    
    listAll();		/* show all records*/  
    printf("Enter contact account number to delete: ");
    scanf("%d",&record);

    currentc = firstc;
    
    while(currentc != NULL)
    {
        if(currentc->number == record)
	{
	    if(currentc == firstc)	/*if record to be deleted is the first record*/
		firstc=currentc->next; /*reset firstc to point at next record as first*/
	    else
		previousa->next = currentc->next;/*previous pointer used if record*/ 
                                         /*to delete is not the first*/
        free(currentc); /*frees memory <deletes>*/
	    printf("contact %d deleted!\n",record);
	    return;
	}
	
	else
	{
        previousa = currentc;
	    currentc = currentc->next;
	}
    }
    printf("contact %d not found!\n",record);
 }
/*----------------------------------------------------------------------------*/
void modifycontact(void)   /*modify contact function*/
{
    int record, result;

    if(firstc==NULL)
    {
        puts("There are no contacts to modify!");
	return;
    }
    
    listAll();		/* show all records */
    printf("Enter contact account number to modify or change: ");
    scanf("%d",&record);  /*scan user input to record*/

    result = findnum(record);
    
    if( result >0 ){
	    printf("Contact %d:\n",currentc->number);
	    printf("Name: %s\n",currentc->name);
	    if(prompt())
		    gets(currentc->name);
	    printf("Phone: %s\n",currentc->phone);
	    if(prompt())
		    gets(currentc->phone);
	    printf("Email: %s\n",currentc->email);
	    if(prompt())
		    gets(currentc->email);
	    return;
	}
    printf("contact %d was not found!\n",record);
}
/*----------------------------------------------------------------------------*/
int findnum (int recordnum)
{
    int record;
    record = recordnum;
    currentc = firstc;
    while(currentc != NULL)
    {
                   
        if(currentc->number == record)
	     {
           return 1;
         }
         
	else
	{
	    currentc = currentc->next;
	}
    }
    return -1;   
}
/*----------------------------------------------------------------------------*/
int findcontact(void) /* find contact function*/
{
     char buff[20];
     
     if(firstc==NULL)
	{
        puts("There are no contacts to find!");
	    return 1;
    }
    
    printf("Enter contact name: ");
    fflush(stdin);/*clears any text from the input stream*/
    gets(buff);
    
    currentc = firstc;
    while(currentc != NULL)
    {
        if( strcmp(currentc->name, buff) == 0 )
	    {
			printf("%6s %-20s %-15s %-15s\n","Acct#","Name","Phone","Email");
			/*prints table titles*/
            printf("%6d: %-20s %-15s %-20s\n",\
            currentc->number,\
            currentc->name,\
            currentc->phone,\
            currentc->email); 
            /*prints values of number, name, phone and email*/
			
			return 0;
	    }
		else
		{
			currentc = currentc->next;
		}
    }
    printf("contact %s was not found!\n",buff);
          return 1;
}   
/*----------------------------------------------------------------------------*/
int prompt(void)
{
	char ch;

    fflush(stdin);
	printf("Update? (Y to update any other key to not)");
	ch = getchar();
	ch = toupper(ch);
	fflush(stdin);
	if(ch == 'Y')
	{
		printf("Enter new value: ");
		return(1);
	}
	else
		return(0);
}
/*----------------------------------------------------------------------------*/

/* END OF PROGRAM */