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56 lines
1.3 KiB
Markdown
56 lines
1.3 KiB
Markdown
---
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title: "09-intro-to-c-2"
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aliases:
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tags:
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- cosc204
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---
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# Variables and Pointers
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```
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va memory[3]
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*va memory[memory[3]]
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**va memory[memory[memory[3]]]
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```
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`*` is known as **dereferncing**
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`**` is known as **double-dereferncing**
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## Names and places
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names are allocated to emmory locations of declaration
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`&b;` wherever in memory b is stored
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## Why Pointers
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- abstractions
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- dont need to know which "object" to manipulate
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- ability to change a parameter
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- multiple return values from a routine
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- efficiency
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- dont need to copy anything to pass a pointer
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## Call by value
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- The value of the variable is passed to the called routine.
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- changes to the parameter do not propogate to the caller
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## Call by address
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- address of parameter is passed to the rountine
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- changes do propogate back to the caller
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- more efficient because we only need to pass a pointer and not a value
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### Multiple results
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- c routine can return at most one value
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- you can use input parameters which are pointers for "returning" results
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### Arrays
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- strings
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- terminated by "\0"
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- argc, argv[]
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- length specified
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- null terminated
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- array of pointers
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### Pointer arithmetic
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- ++ move a pointer fowards in an array
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- -- move a pointer back in an array
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- these operations are "type aware" and increment (the pointer) by the size of the elements of the array |