# 2.5 Functions and pointers  (Page 10/11)

 Page 10 / 11

The value of a is 7

The value of *aPtr is 7

Notice that the address of a and the value of aPtr are identical in the output, confirming that the address of a is assigned to the pointer variable aPtr.

## Calling functions by reference with pointer arguments

In C++, programmers can use pointers and the dereference operator to simulate call-by-reference. When calling a function with arguments should be modified, the addresses of the arguments are passed. This is normally achieved by applying the address-of operator (&) to the name of the variable whose value will be used. A function receiving an address as an argument must define a pointer parameter to receive the address.

Example

`// Cube a variable using call-by-reference`

`// with a pointer argument`

`#include<iostream.h>`

`void cubeByReference( int * ); // prototype`

`int main()`

`{`

`int number = 5;`

`cout<<"The original value of number is "<<number;`

`cubeByReference(&number );`

`cout<<"\nThe new value of number is "<<number<<endl;`

`return 0;`

`}`

`void cubeByReference( int *nPtr )`

`{`

`*nPtr = (*nPtr) * (*nPtr) * (*nPtr); // cube number in main`

`}`

The output of the above propgram:

The original value of number is 5

The new value of number is 125

## Pointers and arrays

Notice that the name of an array by itself is equivalent to the base address of that array. That is, the name z in isolation is equivalent to the expression&z[0].

Example

`#include<iostream.h>`

`int main()`

`{`

`int z[] = { 1, 2, 3, 4, 5};`

`cout<<“The value return by ‘z’ itself is`

`the addr “<<z<<endl;`

`cout<<“The address of the 0th element of`

`z is “<<&z[0]<<endl;`

`return 0;`

`}`

The output of the above program:

The value return by ‘z’ itself is the addr 0x0065FDF4

The address of the 0th element of z is 0x0065FDF4

Accessing Array Element Using Pointer and Offset

Now, let us store the address of array element 0 in a pointer. Then using the indirection operator, *, we can use the address in the pointer to access each array element.

For example, if we store the address of grade[0] into a pointer named gPtr, then the expression *gPtr refers to grade[0].

One unique feature of pointers is that offset may be included in pointer expression.

For example, the expression *(gPtr + 3) refers to the variable that is three (elements) beyond the variable pointed to by gPtr.

The number 3 in the pointer expression is an offset. So gPtr + 3 points to the element grade[3] of the grade array.

Example

`#include<iostream.h>`

`int main()`

`{`

`int b[] = { 10, 20, 30, 40 }, i, offset;`

`int *bPtr = b; // set bPtr to point to array b`

`cout<<"Array b printed with:\n"`

`<<"Array subscript notation\n";`

`for ( i = 0; i<4; i++ )`

`cout<<"b["<<i<<"] = "<<b[ i ]<<'\n';`

`cout<<"\nPointer/offset notation\n";`

`for ( offset = 0; offset<4; offset++ )`

`cout<<"*(bPtr + "<<offset<<") = "`

`<<*( bPtr + offset )<<'\n';`

`return 0;`

`}`

The output of the above program is:

Array b printed with:

Array subscript notation

b[0] = 10

b[1] = 20

b[2] = 30

b[3] = 40

Pointer/offset notation

*(bPtr + 0) = 10

*(bPtr + 1) = 20

*(bPtr + 2) = 30

*(bPtr + 3) = 40

## Pointers and strings

In C++ we often use character arrays to represent strings. A string is an array of characters ending in a null character (‘\0’). Therefore, we can scan through a string by using a pointer. Thus, in C++, it is appropriate to say that a string is a constant pointer – a pointer to the string’s first character.

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research.net
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or in general
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in general
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On having this app for quite a bit time, Haven't realised there's a chat room in it.
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