Tricky C Programs

Hello friends,

Here i have given some basic programs to understand pointer to array and pointer to string.
copy each and run it on your machine one bye one and see the difference between each of them.

1. Array with Pointer
* Predict the output of following programs.

1.1
main()
{
int arr[]={10,20,40,50,45};
int i;
for(i=0;i<5;i++)
printf("%d ",*(arr+i));
}
-------------------------------------------------------------------
many people have question, what is the difference between array name and pointer to that array?
Run program 1.2 and 1.3 and get the answer by your self.

1.2
main()
{
int arr[]={10,20,40,50,45};
int i;
for(i=0;i<5;i++)
printf("%d ",*(arr++));
}
-------------------------------------------------------------------
1.3
main()
{
int arr[]={10,20,40,50,45},*ptr;
int i;
ptr = arr;
for(i=0;i<5;i++)
printf("%d ",*(ptr++));
}
--------------------------------------------------------------------
1.3 and 1.4 shows the importance of bracket ' ( ) ' .

1.4
main()
{
int arr[]={10,20,40,50,45},*ptr;
int i;
ptr = arr;
for(i=0;i<5;i++)
printf("%d ",(*ptr)++);
}
---------------------------------------------------------------------
1.5
main()
{
int arr[]={10,20,40,50,45},*ptr;
int i;
ptr = arr;
for(i=0;i<5;i++)
printf("%d ",*ptr++);
}

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2. String and Pointer :

2.1

void main()

{

char arr[] = "hello world !!!";

printf("%s\n",arr);

}

------------------------------------------------------------------------

2.2

void main()

{

char *ptr;

ptr = "hello world !!!";

printf("%s\n",ptr);

}

------------------------------------------------------------------------

2.3

void main()

{

char *ptr;

scanf("%s",ptr);                             // input any string.

printf("%s\n",ptr);

}

------------------------------------------------------------------------------------------

In program 2.3 you will get segmentation fault during run time. why?

because when you compile your program compiler decides howmuch space this program will require for execution and for storing variables and all.

In 2.1 and 2.2 compiler automatically calculates the space for given string because the string is already given. but in 2.3,we are entering string during run time and compiler didn't give us any space to store our string. so during run time it gives segmentation fault. In this case we have to use dynamic memory allocation. see example 2.4....

------------------------------------------------------------------------------------------

2.4

void main()

{

char *ptr; = (char *)malloc(5*sizeof(char));

scanf("%s",ptr);                             //  input "hello" or any string with max 5 char.

printf("%s\n",ptr);

}

----------------------------------------------------------------------

i think, these programs are enough to understand pointer to array and pointer to string.

for any query or explanation please use comment box.

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Link for Pointer in C :
http://letsmakeceasy.blogspot.in/2014/09/pointer-in-c.html

Link for Array in C :
http://letsmakeceasy.blogspot.in/2014/09/array-in-c.html

Link for Preprocessor in C :
http://letsmakeceasy.blogspot.in/2014/09/preprocessor-directives.html

Thanks

Akash Patel.