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Lecture 8: Continued Functions

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Reading Assigned:   None

Homework Due:  Homework 03

Homework Assigned:  Homework 04

Classwork Assigned:  Classwork 05

Topics Covered:

• Reminder about using script
• Feedback on course
• Homework 3 review - questions
• Classwork 5 - Functions
• Functions
  • Arguments
  • Return value
  • Variables inside functions
  • Forward declarations
  • Example of incorrect ordering of functions
  • Result of trying to compile:

    linux1[23]% gcc -Wall func_order_bad.c -o func_order_bad
    func_order_bad.c: In function ‘main’:
    func_order_bad.c:12: warning: implicit declaration of function ‘func1’
    func_order_bad.c:13: warning: implicit declaration of function ‘func2’
    func_order_bad.c: At top level:
    func_order_bad.c:17: warning: conflicting types for ‘func1’
    func_order_bad.c:12: note: previous implicit declaration of ‘func1’ was here
    func_order_bad.c:22: warning: conflicting types for ‘func2’
    func_order_bad.c:13: note: previous implicit declaration of ‘func2’ was here
    

  • Example of correct ordering of functions
  • Result of trying to compile:

    linux1[26]% gcc -Wall func_order_good.c -o func_order_good
    linux1[27]% ./func_order_good
    Function 1 called
    Function 2 called
    

  • Example of function forward declaration

    linux1[30]% gcc -Wall func_forward_dec.c -o func_forward_dec
    linux1[31]% ./func_forward_dec
    Function 1 called
    Function 2 called
    

  • Declaration - tells compiler the return value, name, and arguments
  • Definition - tells compiler the implementation of a declared function
  • Declaration and definition can (and often do) occur at the same time, but don't need to
  • BUT -- if they occur at different points, the function signature must match
  • Example of function declarations that don't match

    linux1[38]% gcc -Wall func_forward_dec_bad.c -o func_forward_dec_bad
    func_forward_dec_bad.c:33: error: conflicting types for ‘func1’
    func_forward_dec_bad.c:15: note: previous declaration of ‘func1’ was here
    func_forward_dec_bad.c:38: error: conflicting types for ‘func2’
    func_forward_dec_bad.c:16: note: previous declaration of ‘func2’ was here
    

  • Function signature - the set of return value, name, and argument types
  • A more complex function example

    linux1[69]% gcc -Wall func_complex.c -o func_complex
    linux1[70]% ./func_complex
    func2 was passed arg1=10, arg2=20
    func1 was passed arg1=20
    func3 was passed x=7, y=14
    func2 was passed arg1=14, arg2=7
    func1 was passed arg1=7
    func1 was passed arg1=7
    func1 was passed arg1=14