Functions: - using Library functions - writing our own

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Functions- using Library functions- writing
our own
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include ltcmathgt

• a math library
• x pow( 12, 2 )

" function "
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functions

• a math library
• x pow( 12, 2 )
• that's what parenthesis are for!!

sent TO a function
returned FROM a function
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cmath functions
note the value passed TO the function

• Function Description
• abs(x) computes absolute value of x
• sqrt(x) computes square root of x, where x gt0
• pow(x,y) computes xy
• ceil(x) nearest integer larger than x
• floor(x) nearest integer smaller than x
• exp(x) computes ex
• log(x) computes ln x, where x gt0
• log10(x) computes log10x, where xgt0
• sin(x) sine of x, where x is in radians
• cos(x) cosine of x, where x is in radians
• tan(x) tangent of x, where x is in radians

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writing our own

• we can write functions right in our main program
• it involves 6 steps
• why? to isolate code that you want to run
  (call) repeatedly

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Step 1 - think of a good name

• addTwoNumbers( )

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Step 2 - decide what the function needs to do its
job

• addTwoNumbers ( int addend1, int addend2)
• you can name those variables anything you want,
  but you have to specify their type

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Step 3 - what will the function return as a
service?

• int addTwoNumbers (int addend1, int addend2)

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Step 4 - write the function, outside of the main
brackets

• include ltiostreamgt
• using namespace std
• int main ( )
• int addTwoNumbers ( int addend1, int addend2 )
• int sum 0
• sum addend1 addend2
• return sum

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Step 5 - Introduce it to main

• include ltiostreamgt
• using namespace std
• int addTwoNumbers ( int addend1, int addend2 )
  
• int main ( )
• int addTwoNumbers ( int addend1, int addend2 )
  
• int sum 0
• sum addend1 addend2
• return sum

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Step 6 - use (call) the function from main

• include ltiostreamgt
• using namespace std
• int addTwoNumbers ( int addend1, int addend2 )
  
• int main ( )
• int x, y 12, z 44
• x addTwoNumbers ( y, z )
• cout ltlt x

note different variables (the "hand-off")
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• include ltiostreamgt
• using namespace std
• int addTwoNumbers ( int addend1, int addend2
  )
• int main ( )
• int x, y 12, z 44
• x addTwoNumbers ( y, z )
• cout ltlt x
• int addTwoNumbers ( int addend1, int addend2
  )
• int sum 0
• sum addend1 addend2
• return sum

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return types

• functions can return ints, doubles, bools, chars,
  strings what if a function doesn't return
  anything?
• void drawLine ( int length )