A pointer is a variable that stores the address of another variable. Pointers allow variables to reference memory locations and access the values stored there. An array is a collection of variables of the same type stored contiguously in memory. Strings in C are arrays of characters terminated by a null character. Pointers can also be used to point to strings by storing the base address of the character array. Multidimensional arrays and manipulating strings are also discussed.

1. An Introduction to Pointers

3. • A pointer(address variable) is a variable whose value is used to point to
another variable.
Ex:
long int x, y;
y = &x;
(assigns address of the long integer variable x to another variable, y.)
Ex:
#include <stdio.h>
main()
{
char c;
int x;
float y;
printf("c: address=0x%p, content=%cn", &c, c);
printf("x: address=0x%p, content=%dn", &x, x);
printf("y: address=0x%p, content=%5.2fn", &y, y);
c = `A';
x = 7;
y = 123.45;
printf("c: address=0x%p, content=%cn", &c, c);
printf("x: address=0x%p, content=%dn", &x, x);
printf("y: address=0x%p, content=%5.2fn", &y, y);
return 0;
}
NOTE: %p, %u, %lu

4. • Pointer has Left value and Right value.
– Left value: address its self
– Right value: which is the content of the pointer, is the address of another variable.
– data-type *pointer-name;
• Ex:
#include <stdio.h>
main()
{
char c, *ptr_c;
int x, *ptr_x;
float y, *ptr_y;
c = `A';
x = 7;
y = 123.45;
printf("c: address=0x%p, content=%cn", &c, c);
printf("x: address=0x%p, content=%dn", &x, x);
printf("y: address=0x%p, content=%5.2fn", &y, y);
ptr_c = &c;
printf("ptr_c: address=0x%p, content=0x%pn", &ptr_c, ptr_c);
printf("*ptr_c => %cn", *ptr_c);
ptr_x = &x;
printf("ptr_x: address=0x%p, content=0x%pn", &ptr_x, ptr_x);
printf("*ptr_x => %dn", *ptr_x);
ptr_y = &y;
printf("ptr_y: address=0x%p, content=0x%pn", &ptr_y, ptr_y);
printf("*ptr_y => %5.2fn", *ptr_y);
return 0;
}

5. Storing Similar Data Items
• array is a collection of variables that are of the same data type.
– data-type Array-Name[Array-Size];
EX:
#include <stdio.h>
main()
{
int i;
int list_int[10];
for (i=0; i<10; i++){
list_int[i] = i + 1;
printf( "list_int[%d] is initialized with %d.n", i, list_int[i]);
}
return 0;
}

6. One dimensionl Array
• One dimensional array
– Int a[10], float x[50], char str[30];
– Int a[10]={12,3,4,65,6,2,3}; int
a[]={1,2,3,4,5,6,7,8};
– Char str[30]=“Hello how well?”;
– ‘0’=null remain

7. Ex:
#include <stdio.h>
main()
{
char array_ch[7] = {`H', `e', `l', `l', `o', `!’};
int i;
for (i=0; i<7; i++)
printf("array_ch[%d] contains: %cn", i, array_ch[i]);
/*--- method I ---*/
printf( "Put all elements together(Method I):n");
for (i=0; i<7; i++)
printf("%c", array_ch[i]);
/*--- method II ---*/
printf( "nPut all elements together(Method II):n");
printf( "%sn", array_ch);
return 0;
}
Ex:
#include <stdio.h>
main()
{
char array_ch[15] = {`C', ` `,
`i', `s', ` `,
`p', `o', `w', `e', `r',
`f', `u', `l', `!', `0'};
int i;
/* array_ch[i] in logical test */
for (i=0; array_ch[i] != `0'; i++)
printf("%c", array_ch[i]);
return 0;
}

8. INSERT, SEARCH, SORT, DELETE in one
demensional Array

9. Multidimensional Arrays
• data-type Array-Name[Array-Size1][Array-
Size2]. . .[Array-SizeN];
– int array_int[2][3];
– int array_int[2][3] = {{1, 2, 3}, {4, 5, 6}};

10. Unsized Arrays
• int list_int[] = { 10, 20, 30, 40, 50, 60, 70, 80, 90};
• char list_ch[][2] = { `7', `A', `b', `B',`c', `C',`d',
`D',`e', `E', `f', `F',`g', `G'};

11. Manipulating Strings
• a string is a character array terminated by a
null character (0).
• char array_ch[7] = {`H', `e', `l', `l', `o', `!', `0'};
• char str[7] = "Hello!";
• char str[] = "I like C.";
• char *ptr_str = "I teach myself C.";

12. • char ch = `x';
• char str[] = "x";
• char *ptr_str;
ptr_str = "A character string.";

13. #include <stdio.h>
main()
{
char str1[] = {`A', ` `,
`s', `t', `r', `i', `n', `g', ` `,
`c', `o', `n', `s', `t', `a', `n', `t', `0'};
char str2[] = "Another string constant";
char *ptr_str;
int i;
/* print out str2 */
for (i=0; str1[i]; i++)
printf("%c", str1[i]);
printf("n");
/* print out str2 */
for (i=0; str2[i]; i++)
printf("%c", str2[i]);
printf("n");
/* assign a string to a pointer */
ptr_str = "Assign a string to a pointer.";
for (i=0; *ptr_str; i++)
printf("%c", *ptr_str++);
return 0;
}

14. #include <stdio.h>
main()
{
char str[80];
int i, delt = `a' - `A';
printf("Enter a string less than 80 characters:n");
gets( str );
i = 0;
while (str[i]){
if ((str[i] >= `a') && (str[i] <= `z'))
str[i] -= delt; /* convert to upper case */
++i;
}
printf("The entered string is (in uppercase):n");
puts( str );
return 0;
}

15. char *str = "Hello World!";
• Alternatively one might think that a pointer to string in C is a pointer to a char array
/ a pointer to a pointer to a char.
• char *str = "Hello World!";
– str is a pointer to a string.
– str is a pointer to a char array.
– But str is a pointer to a char (not a pointer to a pointer to a
char). str is of type char * .(and here str points to H).
– Ended by 0 null
– char *v1=“A”; 2 bytes
– char v1=‘A’; 1 byte
– ‘A’ + 20 + ‘C’ but not “A” + 20 + “C”
H e l l o W o r l ! 0
A 0
A

16. Arr[6]=“12345”;
• char arr[6]=“gfhgf”;
• char arr[6]={‘1’,’2’,’3’,’4’,’5’};
• char arr[]=“3212432432”;
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