A small presentation on Pointers in C ++

A presentation on Pointers

1. Pointers
Dr Rishi Ruttun

2. Learning Outcomes
ComputerMemory
Pointer
WhyPointers?
Pointers’declaration
Pointers’initialisation
Accessingthevalueofavariable
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3. Computer Memory
Thecomputer’smemoryisasequentialcollection
ofstoragecells.
Eachcell,commonlyknownasabyte,hasa
numbercalledaddressassociatedwithit.
Theaddressesarenumbersconsecutively,starting
fromzero.
Thelastaddressdependsonthememorysize.
Acomputersystemwith64Kmemorywillhaveits
lastaddressas65,535.
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4. Variable and Computer Memory
Eachvariableisassignedamemoryslot(thesizedepends
onthedatatype),andthevariable’sdataisstoredthere.
Variable a’ has a value 100, is
stored at memory location 1010
100… …
1010…
Memory address: 1010 1022
int a = 100;
…
1007
a
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5. Sincememoryaddressesaresimplynumbers(i.e.,1007,1010,1022,etc.),theycanbe
assignedtosomevariablesthatcanbestoredinmemory,likeanyothervariable.
Suchvariablesthatholdmemoryaddressesarecalledpointervariables.
Apointervariableisnothingbutavariablethatcontainsanaddress,whichisthelocationof
anothervariableinmemory.
100… …
10101007
Memory address: 1010 1022
…
1007
integer pointer
Pointer variable
int a = 100;
Variable a’ has a value 100, is
stored at memory location 1010
Memory
address
pointer
5
a

6. Why Pointers?
Theyincreasetheexecutionspeedandthusreducethe
program’sexecutiontime.
Theyprovideanefficienttoolformanipulatingdynamic
datastructuressuchasstructures,linkedlists,queues,and
stacks.
Theyareefficientathandlingarraysanddatatables.
.....
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7. AddressOperator
Symbol:&(ampersand)
Feature:Givestheaddressofthevariable
DereferencingorIndirectionOperator
Symbol:*(asterisk)
Feature:Givesthevalueofthevariablethatthepointerispointingto
100… …
10101007
Memory address: 1010 1022
…
1007
integer pointer
Operators in Pointers
int a = 100;
Variable a’ has a value 100, is
stored at memory location 1010
Memory
address
pointer
7
a

8. Pointer declaration
Sincepointervariablescontainaddressesofseparatedata
types(int,float,double,char,etc.),theymustbedeclared
beforewecanusethem.
Syntaxformforpointervariabledeclaration:
Examples
int*p
oDeclaresthevariablepasapointervariablethatpointstoanintegerdatatype
float*p
oDeclaresthevariablepasapointerthatpointstoafloatdatatype
data_type *pt_name
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9. Pointer declaration styles
int*p;//style1//
Int*p;//style2//
Int*p;//style3//
Alloftheabovestylesarethesameinthesensethateach
ofthemisdeclaringapointer.
However,style2ismorepopularasitisconvenientto
havemultipledeclarationswithinthesamestatement:
oE.g.,int*p,z,*t;
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10. PointerInitializationistheprocessofassigningtheaddressofavariableto
apointervariable.
Apointervariablecanonlycontaintheaddressofavariableofthesamedatatype.
Theaddressoperator(&)isusedtodeterminetheaddressofavariable.
E.g.,ptr=&a,whereptrisapointervariableandaisavariable.
100… …
10101007
Memory address: 1010 1022
…
1007
integer pointer
Pointer Initialisation
int a = 100;
Variable a’ has a value 100, is
stored at memory location 1010
Memory
address
pointer
10
a

11. Pointer Initialisation –E.g.
11
C language

12. Wecanaccessthevaluestoredinthevariablepointedtobyusingthe
Dereferencingoperator(*).
Let’sgoforanexampleonthenextslide.
100… …
10101007
Memory address: 1010 1022
…
1007
integer pointer
Accessing the value of a variable using
Pointer
int a = 100;
Variable a’ has a value 100, is
stored at memory location 1010
Memory
address
pointer
12

13. Accessing the value of a variable –E.g.
13
C language

14. Summary
Thecomputer’smemoryisasequentialcollectionofstorage
cells,andeachcellhasanumbercalledanaddressassociated
withit.
Eachvariableisassignedamemoryslot,andthevariable’s
dataisstoredthere.
Apointervariableisavariablethatcontainsanaddress.
Pointersmustbedeclaredbeforewecanusethem.
Pointerinitializationistheprocessofassigningtheaddressofa
variabletoapointervariableusingtheaddressoperator(&).
Adereferencingoperator(*)isusedtoaccessthevaluestored
inthevariablepointedto.
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