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5.1 Pointer

A Pointer is a variable, which contains the address of a memory location of another variable. If one variable contains the address of another variable, the first variable is said to point to the second.
1000 (Memory Location)       50 (Value)        var (Variable Name)

- Used to return more than one value from a function
- To pass arrays and strings.
- To allocate memory and access it.

 type   *name;

 main()
 {
 int var1, *var2, temp;
 var1=500;
 var2= &var1;
 temp=*var2;
 :
 }

5.2 Pointer as function Argument

Pointers are passed to a function to enable data items, within the called routine of the program, to access variables whose scope does not extend beyond the calling function.

#include<stdio.h>
main()
{
void swap(int *u, int  *v);
int x=15, y=20;
printf("x=%d, y=%d\n", x,y);
swap(&x, &y);
printf("\nAfter interchanging x=%d,y=%d\n",x,y);
}
void swap(int  *u, int  *v)
{
int temp;
temp=*u;
*u=*v;
*v=temp;
return;
}

5.3 Array of Pointers

A multidimensional array can be expressed in terms of an array of pointers rather than as a pointers to a group of contiguous arrays.

 int *ptr_ary[10];

6.1 Structures

A Structure consists of a number of a data items, which need not be of the same type, grouped together. A Structure definition forms a template that is used to carry structure variables. The variables that make up the structure are called structure variables.

struct book
{
char bk_name[25];
char author[20];
int edn;
float price;
};

#include<stdio.h>
main()
{
struct
     {
     char name[20];
     int numb;
     float purchase_amt;
     }customer1;
clrscr();
printf("\nEnter Customer Name:");
gets(customer1.name);
printf("\nEnter customer Number:");
scanf("%d",&customer1.numb);
printf("\nEnter Principal Amount:");
scanf("%f", &customer1.purchase_amt);
intcal(customer1);
}
intcal(struct{char cust_name[20];int cust_numb;float amt;}bill)
{
float si;
float rate=5.1;
float yrs = 2.2;
si=(((bill.amt)*rate*yrs))/100;
printf("\nThe Customer Name is %s",bill.cust_name);
printf("\nThe Customer number is %d",bill.cust_numb);
printf("\nThe amount is %f",bill.amt);
printf("\n The interest is %f",si);
return;
}

6.2 Array of Structures

One of the most common use of structures is as array of structures. To declare an array of structures, a structure is first defined, and then an array variable of that type is declared.

struct book lost_books[3];

struct unit
{
char ch;
int i;
};
struct unit series[3]=
{
{'a',100}
{'b',200}
{'c',300}
};

6.3 Unions

A Union is same as structure except that union allocates higher memory space used by union variable. A union is a memory location that is shared by two or more variables, generally of different types.

union temp
{
int a;
char ch;
};

7.1 Text Streams and Binary Streams

A text stream is a sequence of characters, which can be organized into lines terminated by a new line character. The new line character is optional on the last line and is determined by the implementation.
A binary stream is a sequence of bytes with a one-to-one correspondence to those in the external device, that is, there are no character translation.

7.2 Basic File Function

fopen()    Opens a file

fclose()   Closes a file
putc()      Writes a character to a file
fputc()     Writes a character from a file
getc()      Reads a character from a file
fgets()     Reads a string from a file
fseek()    Seeks to specified byte in a file
fprintf()    Is to a file what printf() is to the console
fscanf()   Is to a file what scanf() is to the console
feof()       Returns true if EOF reached
ferror()    returns true if an error has occurred
rewind()  Resets the file position locator to the beginning of the file.
remove() Erase a file
fflush()     Flushes a file

7.3 File Pointer (Opening & Closing)

Opening a file

FILE *fp;
fp=fopen("try.c","r");

Closing a file

fclose(FILE *fp);
 

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