Algorithm & programming part VII (Data Structure)

This is 7th part of our meeting. In this meeting we’re gonna talk about pointer. But, before we go to the point , we have to know first about static and dynamic variable. As we know before , we only use static variable to save the data and it can’t be changed when the program is executed. So, static variable is a variable which is the size and sequence can’t be changed when the program is executed. And it is always shown by identifier. On the other hand, Dynamic variable is more flexible, because we can change it’s size and sequence even though the program is executed. And especially for dynamic variable, it’s always shown by pointer.

Pointer is very important for managing memory in a big program. A programmer won’t be a great one if he/ she still doesn’t master pointer first. Because it’s a basic in a structure of a big program.

On the other side, if we wrong to use pointer, it’s gonna mash up our program. It’s usually called access violation.

In this part and later, I am not gonna make sample from Pascal programming language. Because after this i’d like to focus in C programming language. Alright, let’s declare the pointer now.

For example I wanna declare a pointer In integer type.

Int *p;

it means that I declare a dynamic variable (pointer) with type integer. After this, in main program, we have to order an allocation of memory for the pointer. This Is the way

p=(int*)malloc(sizeof (int));

it means that we have ordered an area as large as integer (2 byte) and we save the address in pointer p

oh…ya I almost forget that malloc function is only exist in stdlib header file so we have to declare it first in the beginning of the program.

Here is the example pointer to integer


#include <stdio.h>
#include <stdlib.h>

int main(){
int a,*p;

printf("Program Pointer Ke Integer\n");
p=(int*)malloc(sizeof(int));
puts("Masukkan sebuah angka ke variabel A = ");scanf("%d",&a);
p=&a;
printf("Hasil peng-Copy-an data dari variabel A ke pointer P adalah = %d\n",*p);
return (0);
}

Here is the example pointer to struct

 

#include <stdio.h>
#include <stdlib.h>

typedef struct data{
char lokasi[20];
int luas;
}data;

typedef struct data node;
node *p;

int main(){

system ("clear");
p=(node*)malloc(sizeof(node));
printf("Masukkan nama lokasi sebuah tempat = ");scanf("%s",p->lokasi);
printf("Masukkan luas lokasi tempat tersebut= ");scanf("%d",&p->luas);
printf("Sebelum pointer P dibuat NULL\n");
printf("Nama lokasi tersebut adalah = %s\n",p->lokasi);
printf("Nama luas tersebut adalah = %d\n",p->luas);
free(p);
printf("Sesudah pointer P dibuat NULL\n");
printf("Nama lokasi tersebut adalah = %s\n",p->lokasi);
printf("Nama luas tersebut adalah = %d\n",p->luas);
return (0);
}

 

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