In this last chapter we will learn, how to create a database. First we must make a declaration for a structure:
#define ARRAY_SIZE 100
/* Structure declaration */
struct record{
char name[21];
char tel[15];
};
/* declaration of array of structure */
struct record array[ARRAY_SIZE];/* max. 100 records*/
Next we must write the file by reading one record at a time.
i=0;
fread (&array[i], sizeof(struct record),1, file);
while (!feof(file) && i<ARRAY_SIZE-1)
{
i++;
fread (&array[i],sizeof(struct record),1, file);
extern int nmb = i;/*nmb must be a global variable*/
}
After the array is ready to copy to the file, it can be done by using fwrite-function:
fwrite(array, sizeof (struct record), nmb, file) /*nmb is the number of records in array*/
Next example (written in finnish) shows, how program reads 10 integers in array, sorts them and after that prints them. This example doesn’t write the data into a file!
#include<stdio.h>
/* SYMBOLIC CONSTANTS*************/
#define KOKO 10/*SIZE OF THE ARRAY*/
/* PROTOTYPES FOR FUNCTIONS *********/
void tayta_taulukko (void);/*fills the array*/
void tulosta_taulukko (void);/prints the array*/
void lajittele_taulukko (void);/*sorts the array*/
void vaihda (int *, int *);/*swaps the numbers in ascending order)
/* GLOBAL VARIABLES ************/
int taulukko[KOKO];/*taulukko= array*/
/* MAIN PROGRAM********************/
void main (void)
{
tayta_taulukko();
lajittele_taulukko();
tulosta_taulukko();
}
/* FUNCTION DECLARATIONS***********/
void tayta_taulukko (void)
{
int i;
for (i=0; i<KOKO; i++)
{
printf ("Enter integer : ");
scanf ("%d",&taulukko[i]);
}
}
void tulosta_taulukko (void)
{
int i;
for (i=0; i<KOKO; i++)
{
printf ("%d\n",taulukko[i]);
}
}
void lajittele_taulukko (void)
{
int i,j,pienin;/* pienin=smallest*/
for (i=0; i < KOKO-1; i++)
{
pienin = i;
for (j=i+1; j < KOKO; j++)
{
if (taulukko[j] < taulukko[pienin])
{
pienin = j;
}
}
if (pienin != i)
{
vaihda (&taulukko[i], &taulukko[pienin]);
}
}
}
void vaihda (int *x, int *y)
{
int apu;
apu = *x;
*x = *y;
*y = apu;
}
Let’s continue with files. Next example shows how to copy one file to another.
/*reduce: copies one file */
#include
main(argc, argv)
int argc;
char *argv[];
{
FILE *In, *Out;
int charac;
int number=0;
static char name[20];
if(argc < 2)
printf("I need a filename for argument\n");
else
{
if ((In = fopen(argv[1], "r")) != NULL )
{
strcpy(name, argv[1]);
strcat(name,".red");
Out=fopen(name, "w");
while((charac=getc(In)) != EOF)
/*if(number++%3 ==0) what happens if you add this to your code?*/
putc(charac,stdout);
fclose(In);
fclose(Out);
}
else
printf("Cannot open file \"%s.\".\n", argv[1]);
}
}
Usage: type reduce file.txt in command prompt, file should contain some text.
Next example is a database, where the options 3 and 4 are missing. Your task is to write them.
/*Database: Usage of database */
#include <stdio.h>
#define NAME_MAX 20
main(number,names) /*HERE STARTS MAIN*/
int number;
char *names[];
struct record{
char name[21];
char tel[15];
};
{
struct record r;
char line[81];
FILE *In;
char contacts[20];
char answer;
int selection;
do{
printf("\nDatabase program, please select:");
printf("\n1. Add the data");
printf("\n2. Print the data");
printf("\n3. Update the data, not in use");
printf("\n4. Remove the data, not in use");
printf("\n0. Exit");
printf("\nYour choice: ");
scanf("%d", &selection);
getchar();
switch(selection)
{
case 1:
if(number < 2)
puts("I need a filename for argument\n");
else
{
if ((In = fopen(names[1], "wb")) == 0 )
printf("Cannot open! %s.\n", names[1]);
else
{
do{
printf ("\nEnter the name (max %d characters):", NAME_MAX);
gets(r.name);
printf("\nEnter the phonenumber: ");
gets(line);
sscanf(line,"%d",r.tel);
fwrite(&r, sizeof r,1,In);
printf ("\nMore names (y/n)?");
answer = getchar();
getchar();
}while (answer=='y');
}
fclose(In);
}
break;
case 2:
if(number < 2)
puts("I need a filename for argument\n");
else
{
if ((In = fopen(names[1], "rb")) == 0 )
printf("Cannot open! %s.\n", names[1]);
else
{
fread (&r,sizeof r,1,In);
while (!feof(In))
{
printf ("\n%s %d\n",r.name,r.tel);
fread(&r,sizeof r,1,In);
}
}
fclose(In);
}
break;
case 0:
printf("\nYou selected the exit, Goodbye.");
break;
default: printf("\n Enter the right choice! (0, 1, 2)"); break;
}
}while(selection != 0);
}
Usage: Enter Database file.bin in command prompt.
This is a last chapter of C programming. Although we have dealt with many issues, there are a lot of things you can study more. For example recursion, the C preprocessor, miscellaneous functions, command line arguments etc. These issues you can study from the C Programming Language by Ritchie Kernigham. Hopefully you have enjoyed the course and specially learned a lot.
NOTE! This chapter exercises can be found in quiz exercises to chapter 9 This information will be tested in quizzes 7-9 It is very important that the student will make all examples shown in this chapter.