Use of Pointers

How use of pointer increases Execution Speed?

It is says that use of pointers will increase the speed of execution. Well it depends on the how and where we are using it.  When we use a pointer to access a variable then first program goes to the memory address of variable and then goes to variable. We will understand the execution time by taking two cases in consideration. First with passing single variable to a function and second with passing array of data to function.

Case 1: Passing Single variable to another function

Figure below show an example of finding square of a number by call by reference function :

      int value1=50;               //value1 defination

      int *ptr1;                     // pointer defination

      int value2=0;                          //value2 defination

      ptr1=&value1;               // copy value1 address to pointer ptr1

      value2=fuction1(ptr1);     // call of function for square a value

.

.

     /***function for square of a number*****/

     int function1(int *pointer)

    {int a=0;

     a=*pointer;

     return(a*a);}

value1 address will be stored in pointer ptr1. Square of a no is found by passing the value1 to function1 using call by reference. Function1 will calculate the square of the no and return the value to value2. I this before calling function1 cpu calculate the address of value1 and pass it to function. In function1 cpu first go to address, then find value at this location and then calculate the square of number. 

If we execute this function using call by value then program will be like this:

    int value1=50;               //value1 defination

    int value2=0;                          //value2 defination

    value2=fuction1(value1);  // call of function for square a value

    .

    .

    /***function for square of a number*****/

   int function1(int value)

  {

    return(value*value);}

It will transfer the value directly to function1. In function1 value1 will be copied to value, calculate the square of no and then return value to value2.

So call by value will take less time to execute this and program size will be small. So for such type of operation call by value method will be preferred.

Case 2: Passing array of data to function.

Figure below show the example of passing an array of data to function and then return average of array data using call by value:

int data[5]={50,40,34,23,78};           //5 byte array defination

int avg_value=0;                            // avg_value variable decleration

avg_value = avg_fun(data[0], data[1],data[2],data[3],data[4]);                                                                //function call by value     

.

.

/***function for average of a number*****/

int function1(int data1, int data2, int data3,int data4, int data5)

{

Int avg=0;

avg=(data1+data2+data3+data4+data5)/5;

return(avg);

}

As per above program if we pass multiple of data from one function to another function it will copied individually in the different location in stack. CPU accesses the data from the stack memory and takes average of data and return result to avg_data.

If we execute this function using pointer it will be like this:

int data[5]={50,40,34,23,78};           //5 byte array definition

int *ptr1;

int avg_value=0;                            // avg_value variable declaration

ptr1=&data;

avg_value = avg_fun(ptr1);                    //function call by value

.

.

/***function for average of a number*****/

int avg_fun (int *ptr1)

{

int avg=0;

int index=0;

for(index=0;index<5;index++)

avg=avg + *ptr++;

return(avg);}

In this scenario we only pass the starting address of data array. This data array starting address will be stored in stack memory. Cpu will fetch the data from location using pointers, calculate the average and return the result. So execution time will be less as compare to   call by value procedure. Another advantage of using pointer is that RAM memory used will be less.