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![Pointers
• Pointer to arrays:
• An array is actually very much like pointer.
• We can declare the arrays first element as a[0]
or as int *a because a[0] is an address and *a is
also an address the form of declaration is
equivalent.
• The difference is pointer is a variable and can
appear on the left of the assignment operator
that is lvalue.
• The array name is constant and cannot appear
as the left side of assignment operator.
11](https://image.slidesharecdn.com/pointers-140130105633-phpapp01/85/Pointers-11-320.jpg)
![Pointers
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/* A program to display the contents of array using pointer*/
#include<stdio.h>
main()
{
int a[100];
int i,j,n,*ptr;
printf("nEnter the elements of the arrayn");
scanf("%d",&n);
printf("Enter the array elements");
for(i=0;i< n;i++)
{
scanf("%d",&a[i]);
}
printf("Array element are");
for(ptr=a;ptr<(a+n);ptr++)
{
printf("nValue of stored at address %u",ptr);
}
}
12](https://image.slidesharecdn.com/pointers-140130105633-phpapp01/85/Pointers-12-320.jpg)
![Pointers
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Multi-Dimensional Arrays
int multi[ROWS][COLS];
we can access individual elements of the array multi using either:
multi[row][col]
or
*(*(multi + row) + col)
To understand more fully what is going on, let us replace
*(multi + row)
with X as in:
*(X + col)
Now, from this we see that X is like a pointer since the expression is
de-referenced and we know that col is an integer. The arithmetic being used here
is of a special kind called "pointer arithmetic". That means that, since we are
talking about an integer array, the address pointed to by (i.e. value of) X + col + 1
must be greater than the address X + col by and amount equal to sizeof(int).
13](https://image.slidesharecdn.com/pointers-140130105633-phpapp01/85/Pointers-13-320.jpg)
![Pointers
• Since we know the memory layout for 2 dimensional
arrays, we can determine that in the expression multi +
row as used above, multi + row + 1 must increase by value
an amount equal to that needed to "point to" the next
row, which in this case would be an amount equal to COLS
* sizeof(int).
• That says that if the expression *(*(multi + row) + col) is to
be evaluated correctly at run time, the compiler must
generate code which takes into consideration the value of
COLS, i.e. the 2nd dimension. Because of the equivalence
of the two forms of expression, this is true whether we
are using the pointer expression as here or the array
expression multi[row][col].
14](https://image.slidesharecdn.com/pointers-140130105633-phpapp01/85/Pointers-14-320.jpg)
![Pointers
•
More on Strings
•
Well, we have progressed quite a way in a short time! Let's back up a little and look at what was done in Chapter
3 on copying of strings but in a different light. Consider the following function:
char *my_strcpy(char dest[], char source[])
{
int i = 0;
while (source[i] != '')
{
dest[i] = source[i];
i++;
}
dest[i] = '';
return dest;
}
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Recall that strings are arrays of characters. Here we have chosen to use array notation instead of pointer
notation to do the actual copying. The results are the same, i.e. the string gets copied using this notation just as
accurately as it did before. This raises some interesting points which we will discuss.
•
Since parameters are passed by value, in both the passing of a character pointer or the name of the array as
above, what actually gets passed is the address of the first element of each array. Thus, the numerical value of
the parameter passed is the same whether we use a character pointer or an array name as a parameter. This
would tend to imply that somehow source[i] is the same as *(p+i).
16](https://image.slidesharecdn.com/pointers-140130105633-phpapp01/85/Pointers-16-320.jpg)
![Pointers
•
Pointers to Functions
•
Up to this point we have been discussing pointers to data objects. C also permits
the declaration of pointers to functions. Pointers to functions have a variety of
uses and some of them will be discussed here.
•
Consider the following real problem. You want to write a function that is capable
of sorting virtually any collection of data that can be stored in an array. This
might be an array of strings, or integers, or floats, or even structures. The sorting
algorithm can be the same for all. For example, it could be a simple bubble sort
algorithm, or the more complex shell or quick sort algorithm. We'll use a simple
bubble sort for demonstration purposes.
•
Sedgewick [1] has described the bubble sort using C code by setting up a function
which when passed a pointer to the array would sort it. If we call that function
bubble(), a sort program is described by bubble_1.c, which follow
17](https://image.slidesharecdn.com/pointers-140130105633-phpapp01/85/Pointers-17-320.jpg)
![Pointers
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/* Program bubble_3.c from PTRTUT10.HTM 6/13/97 */
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#include <stdio.h>
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int arr[10] = { 3,6,1,2,3,8,4,1,7,2};
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void bubble(int *p, int N);
int compare(int *m, int *n);
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int main(void)
{
int i;
putchar('
');
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for (i = 0; i < 10; i++)
{
printf("%d ", arr[i]);
}
bubble(arr,10);
putchar('
');
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}
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void bubble(int *p, int N)
{
int i, j, t;
for (i = N-1; i >= 0; i--)
{
for (j = 1; j <= i; j++)
{
if (compare(&p[j-1], &p[j]))
{
t = p[j-1];
p[j-1] = p[j];
p[j] = t;
}
}
}
}
for (i = 0; i < 10; i++)
{
printf("%d ", arr[i]);
}
return 0;
18](https://image.slidesharecdn.com/pointers-140130105633-phpapp01/85/Pointers-18-320.jpg)
![Pointers
• Pointer to arrays:
• An array is actually very much like pointer.
• We can declare the arrays first element as a[0]
or as int *a because a[0] is an address and *a is
also an address the form of declaration is
equivalent.
• The difference is pointer is a variable and can
appear on the left of the assignment operator
that is lvalue.
• The array name is constant and cannot appear
as the left side of assignment operator.
11](/p?url=https%3A%2F%2Fimage.slidesharecdn.com%2Fpointers-140130105633-phpapp01%2F85%2FPointers-11-320.jpg&__src=https%3A%2F%2Fwww.slideshare.net%2Fslideshow%2Fpointers-30629510%2F30629510&__type=image)
![Pointers
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•
/* A program to display the contents of array using pointer*/
#include<stdio.h>
main()
{
int a[100];
int i,j,n,*ptr;
printf("nEnter the elements of the arrayn");
scanf("%d",&n);
printf("Enter the array elements");
for(i=0;i< n;i++)
{
scanf("%d",&a[i]);
}
printf("Array element are");
for(ptr=a;ptr<(a+n);ptr++)
{
printf("nValue of stored at address %u",ptr);
}
}
12](/p?url=https%3A%2F%2Fimage.slidesharecdn.com%2Fpointers-140130105633-phpapp01%2F85%2FPointers-12-320.jpg&__src=https%3A%2F%2Fwww.slideshare.net%2Fslideshow%2Fpointers-30629510%2F30629510&__type=image)
![Pointers
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•
Multi-Dimensional Arrays
int multi[ROWS][COLS];
we can access individual elements of the array multi using either:
multi[row][col]
or
*(*(multi + row) + col)
To understand more fully what is going on, let us replace
*(multi + row)
with X as in:
*(X + col)
Now, from this we see that X is like a pointer since the expression is
de-referenced and we know that col is an integer. The arithmetic being used here
is of a special kind called "pointer arithmetic". That means that, since we are
talking about an integer array, the address pointed to by (i.e. value of) X + col + 1
must be greater than the address X + col by and amount equal to sizeof(int).
13](/p?url=https%3A%2F%2Fimage.slidesharecdn.com%2Fpointers-140130105633-phpapp01%2F85%2FPointers-13-320.jpg&__src=https%3A%2F%2Fwww.slideshare.net%2Fslideshow%2Fpointers-30629510%2F30629510&__type=image)
![Pointers
• Since we know the memory layout for 2 dimensional
arrays, we can determine that in the expression multi +
row as used above, multi + row + 1 must increase by value
an amount equal to that needed to "point to" the next
row, which in this case would be an amount equal to COLS
* sizeof(int).
• That says that if the expression *(*(multi + row) + col) is to
be evaluated correctly at run time, the compiler must
generate code which takes into consideration the value of
COLS, i.e. the 2nd dimension. Because of the equivalence
of the two forms of expression, this is true whether we
are using the pointer expression as here or the array
expression multi[row][col].
14](/p?url=https%3A%2F%2Fimage.slidesharecdn.com%2Fpointers-140130105633-phpapp01%2F85%2FPointers-14-320.jpg&__src=https%3A%2F%2Fwww.slideshare.net%2Fslideshow%2Fpointers-30629510%2F30629510&__type=image)
![Pointers
•
More on Strings
•
Well, we have progressed quite a way in a short time! Let's back up a little and look at what was done in Chapter
3 on copying of strings but in a different light. Consider the following function:
char *my_strcpy(char dest[], char source[])
{
int i = 0;
while (source[i] != '')
{
dest[i] = source[i];
i++;
}
dest[i] = '';
return dest;
}
•
•
•
•
•
•
•
•
•
•
•
•
Recall that strings are arrays of characters. Here we have chosen to use array notation instead of pointer
notation to do the actual copying. The results are the same, i.e. the string gets copied using this notation just as
accurately as it did before. This raises some interesting points which we will discuss.
•
Since parameters are passed by value, in both the passing of a character pointer or the name of the array as
above, what actually gets passed is the address of the first element of each array. Thus, the numerical value of
the parameter passed is the same whether we use a character pointer or an array name as a parameter. This
would tend to imply that somehow source[i] is the same as *(p+i).
16](/p?url=https%3A%2F%2Fimage.slidesharecdn.com%2Fpointers-140130105633-phpapp01%2F85%2FPointers-16-320.jpg&__src=https%3A%2F%2Fwww.slideshare.net%2Fslideshow%2Fpointers-30629510%2F30629510&__type=image)
![Pointers
•
Pointers to Functions
•
Up to this point we have been discussing pointers to data objects. C also permits
the declaration of pointers to functions. Pointers to functions have a variety of
uses and some of them will be discussed here.
•
Consider the following real problem. You want to write a function that is capable
of sorting virtually any collection of data that can be stored in an array. This
might be an array of strings, or integers, or floats, or even structures. The sorting
algorithm can be the same for all. For example, it could be a simple bubble sort
algorithm, or the more complex shell or quick sort algorithm. We'll use a simple
bubble sort for demonstration purposes.
•
Sedgewick [1] has described the bubble sort using C code by setting up a function
which when passed a pointer to the array would sort it. If we call that function
bubble(), a sort program is described by bubble_1.c, which follow
17](/p?url=https%3A%2F%2Fimage.slidesharecdn.com%2Fpointers-140130105633-phpapp01%2F85%2FPointers-17-320.jpg&__src=https%3A%2F%2Fwww.slideshare.net%2Fslideshow%2Fpointers-30629510%2F30629510&__type=image)
![Pointers
•
/* Program bubble_3.c from PTRTUT10.HTM 6/13/97 */
•
#include <stdio.h>
•
int arr[10] = { 3,6,1,2,3,8,4,1,7,2};
•
•
void bubble(int *p, int N);
int compare(int *m, int *n);
•
•
•
•
•
int main(void)
{
int i;
putchar('
');
•
•
•
•
•
•
•
for (i = 0; i < 10; i++)
{
printf("%d ", arr[i]);
}
bubble(arr,10);
putchar('
');
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}
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void bubble(int *p, int N)
{
int i, j, t;
for (i = N-1; i >= 0; i--)
{
for (j = 1; j <= i; j++)
{
if (compare(&p[j-1], &p[j]))
{
t = p[j-1];
p[j-1] = p[j];
p[j] = t;
}
}
}
}
for (i = 0; i < 10; i++)
{
printf("%d ", arr[i]);
}
return 0;
18](/p?url=https%3A%2F%2Fimage.slidesharecdn.com%2Fpointers-140130105633-phpapp01%2F85%2FPointers-18-320.jpg&__src=https%3A%2F%2Fwww.slideshare.net%2Fslideshow%2Fpointers-30629510%2F30629510&__type=image)
Uploaded byFrijo Francis
Pointers
A pointer is a variable that stores the memory address of another variable. Pointers allow accessing and modifying the data stored at the referenced memory location. Pointers can be declared by specifying the data type followed by an asterisk, and are initialized by assigning the address of a variable to the pointer variable. Pointer variables can be used in expressions and arithmetic and can be passed to functions to modify the referenced data. Arrays can also be accessed and traversed using pointers by treating the array name as a pointer to its first element. Pointers to functions allow functions to be passed as arguments and enables polymorphism.
