Engineering Problem Solving with C Fundamental Concepts

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Engineering Problem Solving with C Fundamental
Concepts

• Chapter 4
• Modular Programming with Functions

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Modularity
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Modularity

• Execution of a program begins in the main
  function
• The main function can call other functions
• Functions defined in the same file
• Function defined in other files or libraries
• Functions are also referred to as modules
• A module is a set of statements that performs a
  task or computes a value

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Advantages of using modules

• Modules can be written and tested separately
• Large projects can be developed in parallel
• Reduces length of program, making it more
  readable
• Promotes the concept of abstraction

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Programmer Defined Functions
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Functions

• Defined to
• return a single value to the calling function
• perform a task
• change the value of the function arguments (call
  by reference)

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Functions

• Pre-defined
• standard libraries
• Programmer defined

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Pre-defined FunctionsExample
include ltstdlib.hgt include ltmath.hgt int
main(void) double angle printf( input
angle in radians \n) scanf(1f, angle)
printf( \nthe sine of the angle is
f\n,sin(angle) ) return 0 //end main
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Programmer Defined FunctionsTerminology

• Function Prototype
• describes how a function is called
• Function Call
• Actual parameter
• used in the function call
• Function Definition
• Formal Parameters
• used in function definition
• Formal parameters must match with actual
  parameters in order, number and data type.

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Value Returning Functions

• Function returns a single value to the calling
  program
• Function definition declares the type of value to
  be returned
• A return expression statement is required in the
  function definition

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Example - factorial function
/function definition n! n(n-1)(n-2)1, 0!
1 by definition - fact returns n! assumes
n is non-negative integer / int fact(int n)
int fact 1 while(ngt1) fact
factn n-- //end while block
return(fact) //end fact
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Function prototype - prototype can be included
with preprocessor directives, or with variable
declarations.
include ltstdlib.hgt int main(void) / Declare
variables and function prototypes. / int n
int fact(int n) printf(Enter a positive
integer\n) scanf("i, n) if(ngt0) printf(
i! is i\n, n, fact(n) ) return
0 Note In this example the function fact is
called in the printf statement.
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Calling a function - the value returned by a
function can be assigned to a variable, printed,
or used in an expression
include ltstdlib.hgt int main() /Declare
variables and function prototypes / int
fact(int) int n, factorial printf(enter
positive integer\n) scanf(lf,n) if(ngt0)
factorial fact(n) printf(i! is
i\n, n , factorial) return 0
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void Functions

• A void function may be called to
• perform a particular task (clear the screen)
• modify data
• perform input and output
• A void function does not return a value to the
  calling program
• if a return statement is used (no return value)

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Example of void function definition

• void print_date(int mo, int day, int year)
• /output formatted date /
• printf(iii\n, mo , day , year )
• return

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Parameter Passing

• Call by value
• formal parameter receives the value of the actual
  parameter
• function can not change the value of the actual
  parameter (arrays are an exception)
• Call by reference
• actual parameters are pointers (pointers will be
  discussed in chapter 6)

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Storage Class and Scope

• Scope refers to the portion of the program in
  which it is valid to reference a function or a
  variable
• Storage class refers to the lifetime of a variable

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Scope

• Local scope - a local variable is defined within
  a function or a block and can be accessed only
  within the function or block that defines it
• Global scope - a global variable is defined
  outside the main function and can be accessed by
  any function within the program file.

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Storage Class - 4 types

• automatic - key word auto - default for local
  variables
• Memory set aside for local variables is not
  reserved when the block in which the local
  variable was defined is exited.
• external - key word extern - used for global
  variables
• Memory is reserved for a global variable
  throughout the execution life of the program.
• static - key word static
• Requests that memory for a local variable be
  reserved throughout the execution life of the
  program. The static storage class does not
  affect the scope of the variable.
• register - key word register
• Requests that a variable should be placed in a
  high speed memory register.