B142L Computing practical – Using functions

Academic year 2009/10

Learning outcomes

Practice using functions for the purposes of code re-use, data conversion and logic design.
Become familiar with function prototypes, return type, parameters and function definitions.
Become familiar with the transfer of control sequence as functions are called within a C program.
Practice using pseudo code and D structures to document program design.

Exercise 1: Multiplication tables

Following is part of a program that displays multiplication tables using a user defined function, multTable().

Add the function prototype.
Call the function to display multiplication tables from 1 to 20.

#include <stdio.h>

/* Add prototype here for multTable() function */

int main( void )

{

   /* Call multTable() function here to display multiplication tables */

}

/* Below is the definition for multTable() function */

void multTable( int number )

{

   int counter;

   for ( counter = 1; counter <= 10; counter++ )

      printf( "%2d x %2d = %3d \n", number, counter, number * counter ); 

}

#include <stdio.h>

void multTable( int );

int main( void )

{

   multTable( 1 );

   multTable( 2 );

   multTable( 3 );

   multTable( 4 );

   multTable( 5 );

   multTable( 6 );

   multTable( 7 );

   multTable( 8 );

   multTable( 9 );

   multTable( 10 );

   multTable( 11 );

   multTable( 12 );

   multTable( 13 );

   multTable( 14 );

   multTable( 15 );

   multTable( 16 );

   multTable( 17 );

   multTable( 18 );

   multTable( 19 );

   multTable( 20 );

}

void multTable( int number )

{

   int counter;

   for ( counter = 1; counter <= 10; counter++ )

      printf( "%2d x %2d = %3d \n", number, counter, number * counter ); 

}

Exercise 2: Pythagoras' theorem

Following is part of a program that uses Pythagoras' theorem to determine whether 3 sides form a right triangle.

Add the definition for the testTheorem() function.
The program should read 3 input numbers from stdin and call the function to test the theorem.
The program should end when any one of the input numbers is zero.

Details about Pythagoras' theorem is available online:

http://en.wikipedia.org/wiki/Pythagorean_theorem

#include <stdio.h>

void testTheorem( int, int, int );

int main( void )

{

}

Following is sample output when the input values are 3,4,5 3,5,6 5,12,13 6,12,14 0,1,1.

3, 4 and 5 form a right triangle.

3, 5 and 6 do NOT form a right triangle.

5, 12 and 13 form a right triangle.

6, 12 and 14 do NOT form a right triangle.

0, 1 and 1 form a right triangle.

#include <stdio.h>

void testTheorem( int, int, int );

int main( void )

{

   int n1, n2, n3;

   do

   {

      scanf( "%d,%d,%d", &n1, &n2, &n3 );

      testTheorem( n1, n2, n3 );

   } while ( ( n1 != 0 ) && ( n2 != 0 ) && ( n3 != 0 ) );

}

void testTheorem( int a, int b, int c )

{

   if ( ( ( a * a ) + ( b * b ) ) == ( c * c ) )

      printf( "%d, %d and %d form a right triangle.\n", a, b, c );

   else

      printf( "%d, %d and %d do NOT form a right triangle.\n", a, b, c );

}

Exercise 3: Car parking fees

Write a C program that has at least one user defined function to calculate car parking fees according to the following schedule of rates:

Weekday rates
- First 2 hours is £5.00 per hour
- Each hour after the first 2 hours is £4.50 per hour
Weekend rates
- First 2 hours is £4.50 per hour
- Each hour after the first 2 hours is £4.25 per hour

The program should accept integer input values as comma separated pairs:

number of minutes
1 for weekday rates and zero for weekend rates

Following is sample output when the input values are 90,1 90,0 300,1 300,0 302,1 302,0 0,1.

The parking fee is £9.00 for 90 minutes using weekday rates 

The parking fee is £8.50 for 90 minutes using weekend rates 

The parking fee is £23.50 for 300 minutes using weekday rates 

The parking fee is £21.75 for 300 minutes using weekend rates 

The parking fee is £28.00 for 302 minutes using weekday rates 

The parking fee is £26.00 for 302 minutes using weekend rates

#include <stdio.h>

double carParkFees( int, int );

int main( void )

{

   int minutes, weekday;

   do

   {

      scanf( "%d,%d", &minutes, &weekday );

      if ( minutes != 0 )

      {

         printf( "The parking fee is £%.2lf for %d minutes ", carParkFees( minutes, weekday ), minutes );

         if ( weekday == 1 )

            printf( "using weekday rates \n" );

         else

            printf( "using weekend rates \n" );

      }

   } while ( minutes != 0 );

}

double carParkFees( int feesMinutes, int feesRate )

{

   double fees = 0.0;

   int hours = feesMinutes / 60;

   if ( feesMinutes > ( hours * 60 ) )

      hours = hours + 1;

   if ( feesRate == 1 )

   {

      if ( hours > 2 )

      {

         fees = 10.0;

         hours = hours - 2;

      }

      fees = fees + ( hours * 4.5 );

   }

   else

   {

      if ( hours > 2 )

      {

         fees = 9.0;

         hours = hours - 2;

      }

      fees = fees + ( hours * 4.25 );

   }

   return fees;

}