Introduction to algorithms and data structures in C

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Introduction to algorithms and data structures in
C

• jesus.ibanez_at_upf.edu

2
Functions

• Functions are modules with parameters (or
  arguments), statements, and a result
• Why functions?
• Decomposition
• Code reuse

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Functions

• long int factorial(int n)
• int i
• long int f1
• for (inigt2i--)
• ffi
• return f

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Calling functions

• Variable(s) must match the parameter(s)
• Same number, same order, compatible type,
• Names could be different
• How about printf, scanf?
• printf(hello)printf(ad,a)
• Variable-length parameter list
• int printf(char, ) /stdio.h/

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Calling functions

• include ltstdio.hgt
•  
• long int factorial(int n)
• int i
• long int f1
• for (inigt2i--)
• ffi
• return f
•  
• main()
• int x5
• long int res
• resfactorial(x)
• printf("d\n",res)

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Calling functions

• include ltstdio.hgt
• int major(int a, int b)
• if (agtb) return a
• else return b
• main()
• int a3,b5,c
• cmajor(b,a)
• printf("d", c)

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Call by value

• The execution of a function does not affect the
  value of variables passed as parameters
• void increment(int a)
• a
• int main()
• int i1
• increment(i)
• printf("id\n",i) / i1, not 2 /

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Variable scopes

• Declarations must appear at top of their block
• Function block, if/while block, arbitrary block
• Before any non-declaration statements

Will not compile int myftn() int i
10 i int j 12 j
Will compile int myftn() int i 10 i
11 int j 12 j
Will compile int myftn() int i 10 int
j i 11 j 12 j
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Variable scopes

• A scope of a variable is the portion of the
  program where the variable can be recognized
• File scope
• global variables
• Function scope
• local variables, parameters
• Block scope
• local variables

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Variable scopes

• include ltstdio.hgt
• int x / global variable /
• int f(float x) / parameter /
• return 0
• int g()
• int x / local variable /
• return 0
• int main()
• float x / local variable /
• int x / local variable /

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Prototypes and definitions

• A prototype declares a function with a return
  type and a parameter list.
• float power (float a, float b)
• A definition implements the function
• float power (float a, float b)
• float s
• / calculate the power of a and b /
• / put the result into the variable s/
• return s
• The definition must match the prototype

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Prototypes and definitions

• include ltstdio.hgt
•  
• long int factorial(int n)
•  
• main()
• int x5
• long int res
• resfactorial(x)
• printf("d\n",res)
•  
• long int factorial(int n)
• int i
• long int f1
• for (inigt2i--)
• ffi
• return f

Either the prototype or the definition must
appear before the function call
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Functions

• Functions can call functions
• Example

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Functions

• include ltstdio.hgt
•  
• long int factorial(int n)
• int i
• long int f1
• for (inigt2i--)
• ffi
• return f
•  
• long int combinatori(int m, int n)
• return factorial(m)/(factorial(n)factorial(m-n))
  
•  ...

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Functions

• ...
• main()
• int m,n
• printf(Enter m ")
• scanf("d",m)
• printf(Enter n ")
• scanf("d",n)
• printf("d\n",combinatori(m,n))

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Functions (void)

• For functions taking no parameters
• int f(void)
• For functions returning no values
• void g(void)

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Functions (void)

• ...
• void print_result(int m, int n, int c)
• printf("d over d is d\n",m,n,c)
•  
• main()
• int m,n,c
• printf(Enter m ")
• scanf("d",m)
• printf(Enter n ")
• scanf("d",n)
•  
• ccombinatori(m,n)
• print_result(m,n,c)

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Operator precedence
 
 
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Short-cut assignments