Computer Programming Lab 7 Solution

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Computer ProgrammingLab 7 Solution

• Shyh-Kang Jeng
• Department of Electrical Engineering/
• Graduate Institute of Communication Engineering
• National Taiwan University

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Lab Exercise 6 Greatest Common Divisor

• The greatest common divisor (GCD) of two integers
  is the largest integer that evenly divides into
  each of the two integers. Write a function gcd
  that returns the greatest common divisor of two
  integers.

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Sample Output
Enter two integers 6 8 The greatest common
divisor of 6 and 8 is 2 Enter two integers 789
4 The greatest common divisor of 789 and 4 is
1 Enter two integers 9999 27 The greatest
common divisor of 9999 and 27 is 9 Enter two
integers 73652 8 The greatest common divisor of
73652 and 8 is 4 Enter two integers 99 11 The
greatest common divisor of 99 and 11 is 11
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Solution (1/3)

• // CPLab7\Main.cpp
• include ltiostreamgt
• using stdcout
• using stdcin
• using stdendl
• int gcd( int, int )
• int main()
• int a
• int b
• // allow the five sets of numbers to be input
• for ( int j 1 j lt 5 j )
• cout ltlt "Enter two integers "
• cin gtgt a gtgt b

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Solution (2/3)

• cout ltlt "The greatest common divisor of " ltlt a
• ltlt " and " ltlt b ltlt " is "
• ltlt gcd( a, b ) ltlt "\n\n"
• // end for
• return 0
• // end main

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Solution (3/3)

• // function gcd definition
• int gcd( int x, int y )
• int greatest 1
• for( int i 2 i lt ( ( x lt y ) ? x y ) i
  )
• if ( x i 0 y i 0 )
• greatest i
• return greatest
• // end gcd

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Follow-Up Activity 1

• Use global variables to rewrite the program so
  that gcd takes no arguments. Why is it
  considered bad programming practice to use global
  variables?
• Answer Global variables can be referenced from
  anywhere inside a program, hence it is difficult
  to find out where they are changed.

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Follow-Up Activity 1 Solution (1/3)

• // CPLab7\Main.cpp
• include ltiostreamgt
• using stdcout
• using stdcin
• using stdendl
• int a
• int b
• int gcd()
• int main()
• // allow the five sets of numbers to be input
• for ( int j 1 j lt 5 j )
• cout ltlt "Enter two integers "
• cin gtgt a gtgt b

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Follow-Up Activity 1 Solution (2/3)

• cout ltlt "The greatest common divisor of " ltlt a
• ltlt " and " ltlt b ltlt " is "
• ltlt gcd() ltlt "\n\n"
• // end for
• return 0
• // end main

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Follow-Up Activity 1 Solution (3/3)

• // function gcd definition
• int gcd()
• int greatest 1
• for( int i 2 i lt ( ( a lt b ) ? a b ) i
  )
• if ( a i 0 b i 0 )
• greatest i
• return greatest
• // end gcd

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Follow-Up Activity 2

• Create another function called input, that takes
  two integer values passed via call-by-reference
  and replaces their values with two input by the
  user. Use the function to input the values for a
  and b.

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Follow-Up Activity 2 Solution (1/3)

• // CPLab7\Main.cpp
• include ltiostreamgt
• using stdcout
• using stdcin
• using stdendl
• int gcd( int, int )
• void input( int, int )
• int main()
• int a
• int b
• // allow the five sets of numbers to be input
• for ( int j 1 j lt 5 j )
• input( a, b )

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Follow-Up Activity 2 Solution (2/3)

• cout ltlt "The greatest common divisor of " ltlt a
• ltlt " and " ltlt b ltlt " is "
• ltlt gcd( a, b ) ltlt "\n\n"
• // end for
• return 0
• // end main

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Follow-Up Activity 2 Solution (3/3)

• // function input definition
• void input( int x, int y )
• cout ltlt "Enter two integers "
• cin gtgt x gtgt y
• // end input
• // function gcd definition
• int gcd( int x, int y )
• int greatest 1
• for( int i 2 i lt ( ( x lt y ) ? x y ) i
  )
• if ( x i 0 y i 0 )
• greatest i
• return greatest
• // end gcd