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Introduction to Computing – B142L

B142L Computing practical – Using control structures

Academic year 2009/10


Learning outcomes

  1. Evaluate source code and write C programs that use control structures.
  2. Apply logic and math to the design of control structures.
  3. Practice using pseudo code and D structures to document control structures.
  4. Practice using the scanf() function to obtain input.



Exercise 1: Obtain input values


Write a C program to obtain and display input values of the following data types:
#include <stdio.h>

int main( void )
{
   char code;
   int number;
   float value;
   double money;
   
   scanf( "%c %d %f %lf", &code, &number, &value, &money );
   printf( "%c %d %.2f %.2lf", code, number, value, money );
}



There are detailed formatting rules to specify the data type when obtaining input:



An important learning outcome of the unit is the ability to read and use technical documentation. The 4 web links in the above section are required to complete this practical worksheet.



Exercise 2: Handling of spaces


Read the reference information in the section above and determine how spaces are handled when writing C programs that use input values. Write sample programs to test your understanding.
#include <stdio.h>

int main( void )
{
   int code1;
   char code2;
   
   scanf( "%d%c", &code1, &code2 );
   printf( "Found [%d] and [%c] \n", code1, code2 );

   scanf( "%d %c", &code1, &code2 );
   printf( "Found [%d] and [%c] \n", code1, code2 );
   
   scanf( "%d       %c", &code1, &code2 );
   printf( "Found [%d] and [%c] \n", code1, code2 );

   scanf( "%d", &code1 );
   scanf( "%c", &code2 );
   printf( "Found [%d] and [%c] \n", code1, code2 );
}



Exercise 3: Vending machine selection by number


Let's consider a vending machine that has sells 10 different sweets and candy:
  1. Mars
  2. Snickers
  3. Bounty
  4. Peanut M&M
  5. Chocolate M&M
  6. Aero Bubbles
  7. Fruit Pastilles
  8. Wine Gums
  9. Polo mints
  10. Haribo Gold Bears

Write a C program that display a message corresponding to the candy selected by the user.

Following is a sample output display when the user input is number 4
You selected Peanut M&M

#include <stdio.h>

int main( void )
{
   int candy;
   
   scanf( "%d", &candy );
   
   if ( candy == 1 )  printf( "You selected Mars" );
   if ( candy == 2 )  printf( "You selected Snickers" );
   if ( candy == 3 )  printf( "You selected Bounty" );
   if ( candy == 4 )  printf( "You selected Peanut M&M" );
   if ( candy == 5 )  printf( "You selected Chocolate M&M" );
   if ( candy == 6 )  printf( "You selected Aero Bubbles" );
   if ( candy == 7 )  printf( "You selected Fruit Pastilles" );
   if ( candy == 8 )  printf( "You selected Wine Gums" );
   if ( candy == 9 )  printf( "You selected Polo mints" );
   if ( candy == 10 ) printf( "You selected Haribo Gold Bears" );
}



Exercise 4: Vending machine selection by character


Let's change the list of sweets and candy to characters:
  1. Mars
  2. Snickers
  3. Bounty
  4. Peanut M&M
  5. Chocolate M&M
  6. Aero Bubbles
  7. Fruit Pastilles
  8. Wine Gums
  9. Polo mints
  10. Haribo Gold Bears

Write a C program that display a message corresponding to the candy selected by the user.

Following is a sample output display when the user input is character c
You selected Bounty

#include <stdio.h>

int main( void )
{
   char candy;
   
   scanf( "%c", &candy );
   
   if ( candy == 'a' ) printf( "You selected Mars" );
   if ( candy == 'b' ) printf( "You selected Snickers" );
   if ( candy == 'c' ) printf( "You selected Bounty" );
   if ( candy == 'd' ) printf( "You selected Peanut M&M" );
   if ( candy == 'e' ) printf( "You selected Chocolate M&M" );
   if ( candy == 'f' ) printf( "You selected Aero Bubbles" );
   if ( candy == 'g' ) printf( "You selected Fruit Pastilles" );
   if ( candy == 'h' ) printf( "You selected Wine Gums" );
   if ( candy == 'i' ) printf( "You selected Polo mints" );
   if ( candy == 'j' ) printf( "You selected Haribo Gold Bears" );
}



Exercise 5: Handling invalid input values


Add code to your programs for Exercise 3 and 4 to display an informative error message when the user provides invalid input values, e.g. less than 1 or the character z.
#include <stdio.h>

int main( void )
{
   char candy;
   
   scanf( "%c", &candy );
   
   if ( candy == 'a' ) printf( "You selected Mars" );
   else if ( candy == 'b' ) printf( "You selected Snickers" );
   else if ( candy == 'c' ) printf( "You selected Bounty" );
   else if ( candy == 'd' ) printf( "You selected Peanut M&M" );
   else if ( candy == 'e' ) printf( "You selected Chocolate M&M" );
   else if ( candy == 'f' ) printf( "You selected Aero Bubbles" );
   else if ( candy == 'g' ) printf( "You selected Fruit Pastilles" );
   else if ( candy == 'h' ) printf( "You selected Wine Gums" );
   else if ( candy == 'i' ) printf( "You selected Polo mints" );
   else if ( candy == 'j' ) printf( "You selected Haribo Gold Bears" );
   else printf( "Invalid candy selection" );
}



Exercise 6: Vending machine cost


Let's add a cost to each sweet sold by the vending machine:
  1. £0.55   Mars
  2. £0.55   Snickers
  3. £0.55   Bounty
  4. £0.85   Peanut M&M
  5. £0.85   Chocolate M&M
  6. £0.65   Aero Bubbles
  7. £0.55   Fruit Pastilles
  8. £0.55   Wine Gums
  9. £0.45   Polo mints
  10. £0.95   Haribo Gold Bears

Write a C program that accepts 2 input values:

The program should display a message whether there is enough money for the user selection.

Following is a sample output display when the user inputs are character c and amount 1.20
You selected Bounty and there is enough money


Following is a sample output display when the user inputs are character h and amount 0.40
You selected Wine Gums, but, do not have enough money

#include <stdio.h>

int main( void )
{
   char candy;
   float money, price;
   
   scanf( "%c %f", &candy, &money );
   
   if ( candy == 'a' )
   {
      printf( "You selected Mars" );
      price = 0.55;
   }
   else if ( candy == 'b' )
   {
      printf( "You selected Snickers" );
      price = 0.55;
   }
   else if ( candy == 'c' )
   {
      printf( "You selected Bounty" );
      price = 0.55;
   }
   else if ( candy == 'd' )
   {
      printf( "You selected Peanut M&M" );
      price = 0.85;
   }
   else if ( candy == 'e' )
   {
      printf( "You selected Chocolate M&M" );
      price = 0.85;
   }
   else if ( candy == 'f' )
   {
      printf( "You selected Aero Bubbles" );
      price = 0.65;
   }
   else if ( candy == 'g' )
   {
      printf( "You selected Fruit Pastilles" );
      price = 0.55;
   }
   else if ( candy == 'h' )
   {
      printf( "You selected Wine Gums" );
      price = 0.55;
   }
   else if ( candy == 'i' )
   {
      printf( "You selected Polo mints" );
      price = 0.45;
   }
   else if ( candy == 'j' )
   {
      printf( "You selected Haribo Gold Bears" );
      price = 0.95;
   }
   else
   {
      printf( "Invalid candy selection" );
      price = 0.0;
   }
   
   if ( price > 0 )
   {
      if ( money >= price ) printf( " and there is enough money" );
      else printf( ", but, do not have enough money" );
   }
}



Write pseudo code and D structures when designing control structures. They are easier to communicate and revise than source code.



Exercise 7: Vending machine multiple purchases


Using the same list and prices from Exercise 6, write a C program that accepts 2 input values:

The program should display a message about the quantity of sweets that can be purchased by the user.

Following is a sample output display when the user inputs are character c and amount 2.00
You selected Bounty and have enough money to buy 3 bars


Following is a sample output display when the user inputs are character d and amount 4.50
You selected Peanut M&M and have enough money to buy 5 bags


Following is a sample output display when the user inputs are character h and amount 0.40
You selected Wine Gums, but, do not have enough money

#include <stdio.h>

int main( void )
{
   char candy;
   float money, price;
   int quantity;
   
   scanf( "%c %f", &candy, &money );
   
   if ( candy == 'a' )
   {
      printf( "You selected Mars" );
      price = 0.55;
   }
   else if ( candy == 'b' )
   {
      printf( "You selected Snickers" );
      price = 0.55;
   }
   else if ( candy == 'c' )
   {
      printf( "You selected Bounty" );
      price = 0.55;
   }
   else if ( candy == 'd' )
   {
      printf( "You selected Peanut M&M" );
      price = 0.85;
   }
   else if ( candy == 'e' )
   {
      printf( "You selected Chocolate M&M" );
      price = 0.85;
   }
   else if ( candy == 'f' )
   {
      printf( "You selected Aero Bubbles" );
      price = 0.65;
   }
   else if ( candy == 'g' )
   {
      printf( "You selected Fruit Pastilles" );
      price = 0.55;
   }
   else if ( candy == 'h' )
   {
      printf( "You selected Wine Gums" );
      price = 0.55;
   }
   else if ( candy == 'i' )
   {
      printf( "You selected Polo mints" );
      price = 0.45;
   }
   else if ( candy == 'j' )
   {
      printf( "You selected Haribo Gold Bears" );
      price = 0.95;
   }
   else
   {
      printf( "Invalid candy selection" );
      price = 0.0;
   }
   
   if ( price > 0 )
   {
      if ( money >= price )
      {
         quantity = money / price; /* Force down conversion */
         printf( " and have enough money to buy %d bars", quantity );
      }
      else printf( ", but, do not have enough money" );
   }
}



Exercise 8: Vending machine multiple selections


Using the same list and prices from Exercise 6, write a C program that accepts 3 input values:

The program should display a message about whether the user has enough money to purchase both selections of candy.

Following is a sample output display when the user inputs are characters c, d and amount 2.00
You have enough money to buy Bounty and Peanut M&M


Following is a sample output display when the user inputs are characters c, h and amount 1.00
You do not have enough money to buy Bounty and Wine Gums

#include <stdio.h>

int main( void )
{
   char candy, candy1, candy2;
   float money, totalCost = 0;
   
   scanf( "%c %c %f", &candy1, &candy2, &money );

   candy = candy1;
   while ( candy )
   {
      if ( candy == 'a' ) totalCost += 0.55;
      else if ( candy == 'b' ) totalCost += 0.55;
      else if ( candy == 'c' ) totalCost += 0.55;
      else if ( candy == 'd' ) totalCost += 0.85;
      else if ( candy == 'e' ) totalCost += 0.85;
      else if ( candy == 'f' ) totalCost += 0.65;
      else if ( candy == 'g' ) totalCost += 0.55;
      else if ( candy == 'h' ) totalCost += 0.55;
      else if ( candy == 'i' ) totalCost += 0.45;
      else if ( candy == 'j' ) totalCost += 0.95;
      else totalCost = 0;

      if ( candy == candy1 ) candy = candy2;
      else break; /* exit while loop */
   }

   if ( money >= totalCost ) printf( "You have enough money to buy " );
   else printf( "You do not have enough money to buy " );

   candy = candy1;
   while ( candy )
   {
      if ( candy == 'a' ) printf( "Mars" );
      else if ( candy == 'b' ) printf( "Snickers" );
      else if ( candy == 'c' ) printf( "Bounty" );
      else if ( candy == 'd' ) printf( "Peanut M&M" );
      else if ( candy == 'e' ) printf( "Chocolate M&M" );
      else if ( candy == 'f' ) printf( "Aero Bubbles" );
      else if ( candy == 'g' ) printf( "Fruit Pastilles" );
      else if ( candy == 'h' ) printf( "Wine Gums" );
      else if ( candy == 'i' ) printf( "Polo mints" );
      else if ( candy == 'j' ) printf( "Haribo Gold Bears" );
      
      if ( candy == candy1 )
      {
         printf( " and " );
         candy = candy2;
      }
      else
         break; /* exit while loop */
   }
}



Exercise 9: Price check


Using the same list and prices from Exercise 6, write a C program that accepts an input amount and then use a switch statement to display the list of all candy that has the same or lower price than the input amount.

Following is a sample output display when the user input is 0.50
You have enough money to buy one of the following sweets: Polo mints


Following is a sample output display when the user input is 0.55
You have enough money to buy one of the following sweets: Mars, Snickers, Bounty, Fruit Pastilles, Wine Gums, Polo mints


Following is a sample output display when the user input is 0.90
You have enough money to buy one of the following sweets: Mars, Snickers, Bounty, Peanut M&M, Chocolate M&M, Aero Bubbles, Fruit Pastilles, Wine Gums, Polo mints

#include <stdio.h>

int main( void )
{
   float money;
   int pennies;
   
   scanf( "%f", &money );
   pennies = money * 100;

   printf( "You have enough money to buy one of the following sweets: " );

   if ( pennies > 95 ) pennies = 95; /* The most expensive candy */
   switch ( pennies )
   {
      case 95 :
         printf( "Haribo Gold Bears, " );
      case 94 : case 93 : case 92 : case 91 : case 90 :
      case 89 : case 88 : case 87 : case 86 : case 85 :
         printf( "Peanut M&M, Chocolate M&M, " );
      case 84 : case 83 : case 82 : case 81 : case 80 :
      case 79 : case 78 : case 77 : case 76 : case 75 :
      case 74 : case 73 : case 72 : case 71 : case 70 :
      case 69 : case 68 : case 67 : case 66 : case 65 :
         printf( "Aero Bubbles, " );
      case 64 : case 63 : case 62 : case 61 : case 60 :
      case 59 : case 58 : case 57 : case 56 : case 55 :
         printf( "Mars, Snickers, Bounty, Fruit Pastilles, Wine Gums, " );
      case 54 : case 53 : case 52 : case 51 : case 50 :
      case 49 : case 48 : case 47 : case 46 : case 45 :
         printf( "Polo mints" );
   }   
}



Exercise 10: Vending machine price calculator


Using the same list and prices from Exercise 6, write a C program that accepts 5 input values:

The program must use a for loop to display a message about the amount of money required to purchase one of each candy selected by the user.

Following is a sample output display when the user inputs are characters c, d, e, f, h
The price is £3.45 for Bounty, Peanut M&M, Chocolate M&M, Aero Bubbles, Wine Gums


Following is a sample output display when the user inputs are characters d, e, f, h, i
The price is £3.35 for Peanut M&M, Chocolate M&M, Aero Bubbles, Wine Gums, Polo Mints

#include <stdio.h>

int main( void )
{
   char candy, candy1, candy2, candy3, candy4, candy5;
   float totalCost = 0;
   int counter;
   
   scanf( "%c %c %c %c %c", &candy1, &candy2, &candy3, &candy4, &candy5 );

   for ( counter = 1; counter <= 5; counter++ )
   {
      switch( counter )
      {
         case 1 :
            candy = candy1; break;
         case 2 :
            candy = candy2; break;
         case 3 :
            candy = candy3; break;
         case 4 :
            candy = candy4; break;
         case 5 :
            candy = candy5;
      }

      if ( candy == 'a' ) totalCost += 0.55;
      else if ( candy == 'b' ) totalCost += 0.55;
      else if ( candy == 'c' ) totalCost += 0.55;
      else if ( candy == 'd' ) totalCost += 0.85;
      else if ( candy == 'e' ) totalCost += 0.85;
      else if ( candy == 'f' ) totalCost += 0.65;
      else if ( candy == 'g' ) totalCost += 0.55;
      else if ( candy == 'h' ) totalCost += 0.55;
      else if ( candy == 'i' ) totalCost += 0.45;
      else if ( candy == 'j' ) totalCost += 0.95;
   }

   printf( "The price is £%.2f for ", totalCost );

   for ( counter = 1; counter <= 5; counter++ )
   {
      switch( counter )
      {
         case 1 :
            candy = candy1; break;
         case 2 :
            candy = candy2; break;
         case 3 :
            candy = candy3; break;
         case 4 :
            candy = candy4; break;
         case 5 :
            candy = candy5;
      }

      if ( counter != 1 ) printf( ", " );

      if ( candy == 'a' ) printf( "Mars" );
      else if ( candy == 'b' ) printf( "Snickers" );
      else if ( candy == 'c' ) printf( "Bounty" );
      else if ( candy == 'd' ) printf( "Peanut M&M" );
      else if ( candy == 'e' ) printf( "Chocolate M&M" );
      else if ( candy == 'f' ) printf( "Aero Bubbles" );
      else if ( candy == 'g' ) printf( "Fruit Pastilles" );
      else if ( candy == 'h' ) printf( "Wine Gums" );
      else if ( candy == 'i' ) printf( "Polo mints" );
      else if ( candy == 'j' ) printf( "Haribo Gold Bears" );
   }
}



Use a dry run table to manually calculate the variables involved with iterations and loops. This will help to find logic errors.



Exercise 11: Vending machine price calculator


Using the same list, prices and requirements from Exercise 10, write a C program that uses a while loop to display a message about the amount of money required to purchase one of each candy selected by the user.
#include <stdio.h>

int main( void )
{
   char candy, candy1, candy2, candy3, candy4, candy5;
   float totalCost = 0;
   int counter;
   
   scanf( "%c %c %c %c %c", &candy1, &candy2, &candy3, &candy4, &candy5 );

   counter = 1;
   while ( counter <= 5 )
   {
      switch( counter++ )
      {
         case 1 :
            candy = candy1; break;
         case 2 :
            candy = candy2; break;
         case 3 :
            candy = candy3; break;
         case 4 :
            candy = candy4; break;
         case 5 :
            candy = candy5;
      }

      if ( candy == 'a' ) totalCost += 0.55;
      else if ( candy == 'b' ) totalCost += 0.55;
      else if ( candy == 'c' ) totalCost += 0.55;
      else if ( candy == 'd' ) totalCost += 0.85;
      else if ( candy == 'e' ) totalCost += 0.85;
      else if ( candy == 'f' ) totalCost += 0.65;
      else if ( candy == 'g' ) totalCost += 0.55;
      else if ( candy == 'h' ) totalCost += 0.55;
      else if ( candy == 'i' ) totalCost += 0.45;
      else if ( candy == 'j' ) totalCost += 0.95;
   }

   printf( "The price is £%.2f for ", totalCost );

   counter = 1;
   while ( counter <= 5 )
   {
      if ( counter != 1 ) printf( ", " );

      switch( counter++ )
      {
         case 1 :
            candy = candy1; break;
         case 2 :
            candy = candy2; break;
         case 3 :
            candy = candy3; break;
         case 4 :
            candy = candy4; break;
         case 5 :
            candy = candy5;
      }

      if ( candy == 'a' ) printf( "Mars" );
      else if ( candy == 'b' ) printf( "Snickers" );
      else if ( candy == 'c' ) printf( "Bounty" );
      else if ( candy == 'd' ) printf( "Peanut M&M" );
      else if ( candy == 'e' ) printf( "Chocolate M&M" );
      else if ( candy == 'f' ) printf( "Aero Bubbles" );
      else if ( candy == 'g' ) printf( "Fruit Pastilles" );
      else if ( candy == 'h' ) printf( "Wine Gums" );
      else if ( candy == 'i' ) printf( "Polo mints" );
      else if ( candy == 'j' ) printf( "Haribo Gold Bears" );
   }
}



Exercise 12: Vending machine price calculator


Using the same list, prices and requirements from Exercise 10, write a C program that uses a do/while loop to display a message about the amount of money required to purchase one of each candy selected by the user.
#include <stdio.h>

int main( void )
{
   char candy, candy1, candy2, candy3, candy4, candy5;
   float totalCost = 0;
   int counter;
   
   scanf( "%c %c %c %c %c", &candy1, &candy2, &candy3, &candy4, &candy5 );

   counter = 1;
   do
   {
      switch( counter++ )
      {
         case 1 :
            candy = candy1; break;
         case 2 :
            candy = candy2; break;
         case 3 :
            candy = candy3; break;
         case 4 :
            candy = candy4; break;
         case 5 :
            candy = candy5;
      }

      if ( candy == 'a' ) totalCost += 0.55;
      else if ( candy == 'b' ) totalCost += 0.55;
      else if ( candy == 'c' ) totalCost += 0.55;
      else if ( candy == 'd' ) totalCost += 0.85;
      else if ( candy == 'e' ) totalCost += 0.85;
      else if ( candy == 'f' ) totalCost += 0.65;
      else if ( candy == 'g' ) totalCost += 0.55;
      else if ( candy == 'h' ) totalCost += 0.55;
      else if ( candy == 'i' ) totalCost += 0.45;
      else if ( candy == 'j' ) totalCost += 0.95;
   } while ( counter <= 5 );

   printf( "The price is £%.2f for ", totalCost );

   counter = 1;
   do
   {
      if ( counter != 1 ) printf( ", " );

      switch( counter++ )
      {
         case 1 :
            candy = candy1; break;
         case 2 :
            candy = candy2; break;
         case 3 :
            candy = candy3; break;
         case 4 :
            candy = candy4; break;
         case 5 :
            candy = candy5;
      }

      if ( candy == 'a' ) printf( "Mars" );
      else if ( candy == 'b' ) printf( "Snickers" );
      else if ( candy == 'c' ) printf( "Bounty" );
      else if ( candy == 'd' ) printf( "Peanut M&M" );
      else if ( candy == 'e' ) printf( "Chocolate M&M" );
      else if ( candy == 'f' ) printf( "Aero Bubbles" );
      else if ( candy == 'g' ) printf( "Fruit Pastilles" );
      else if ( candy == 'h' ) printf( "Wine Gums" );
      else if ( candy == 'i' ) printf( "Polo mints" );
      else if ( candy == 'j' ) printf( "Haribo Gold Bears" );
   } while ( counter <= 5 );
}



Exercise 13: Mixed vending selection


Using the same list and prices from Exercise 6, write a C program that accepts an input amount and then uses a sentinel controlled while loop to display a list of all candy that can be bought for the input amount and the amount of change remaining.

Following is a sample output display when the user input is 1.70
You have enough money to buy Mars, Snickers, Bounty with change of £0.05


Following is a sample output display when the user input is 4.00
You have enough money to buy Mars, Snickers, Bounty, Peanut M&M, Chocolate M&M, Aero Bubbles with change of £0.00

#include <stdio.h>

int main( void )
{
   char candy;
   float money;
   int pennies;
   
   scanf( "%f", &money );
   pennies = money * 100; /* convert pounds to pennies */

   if ( pennies >= 45 ) /* Need at least 45 pennies to buy any candy */
   {
      printf( "You have enough money to buy " );

      candy = 'a';
      while ( ( pennies >= 45 ) && ( candy <= 'j' ) ) /* pennies is sentinel variable */
      {
         switch ( candy++ )
         {
            case 'a' :
               if ( pennies >= 55 )
               {
                  printf( "Mars, " );
                  pennies = pennies - 55;
               }
               break;
            case 'b' :
               if ( pennies >= 55 )
               {
                  printf( "Snickers, " );
                  pennies = pennies - 55;
               }
               break;
            case 'c' :
               if ( pennies >= 55 )
               {
                  printf( "Bounty, " );
                  pennies = pennies - 55;
               }
               break;
            case 'd' :
               if ( pennies >= 85 )
               {
                  printf( "Peanut M&M, " );
                  pennies = pennies - 85;
               }
               break;
            case 'e' :
               if ( pennies >= 85 )
               {
                  printf( "Chocolate M&M, " );
                  pennies = pennies - 85;
               }
               break;
            case 'f' :
               if ( pennies >= 65 )
               {
                  printf( "Aero Bubbles, " );
                  pennies = pennies - 65;
               }
               break;
            case 'g' :
               if ( pennies >= 55 )
               {
                  printf( "Fruit Pastilles, " );
                  pennies = pennies - 55;
               }
               break;
            case 'h' :
               if ( pennies >= 55 )
               {
                  printf( "Wine Gums, " );
                  pennies = pennies - 55;
               }
               break;
            case 'i' :
               if ( pennies >= 45 )
               {
                  printf( "Polo mints, " );
                  pennies = pennies - 45;
               }
               break;
            case 'j' :
               if ( pennies >= 95 )
               {
                  printf( "Haribo Gold Bears " );
                  pennies = pennies - 95;
               }
               break;
         }
      }
      
      money = pennies / 100.0; /* convert pennies back to pounds */
      printf( "with change of £%.2f", money );
   }
   else
      printf( "You do not have enough money to buy candy" );
}



Exercise 14: Vending machine price calculator


Using the same requirements from Exercise 13, write a C program that uses a sentinel controlled for loop to display a list of all candy that can be bought for the input amount and the amount of change remaining.
#include <stdio.h>

int main( void )
{
   char candy;
   float money;
   int pennies;
   
   scanf( "%f", &money );
   pennies = money * 100;

   if ( pennies >= 45 ) /* Need at least 45 pennies to buy any candy */
   {
      printf( "You have enough money to buy " );

      for ( candy = 'a'; ( ( pennies >= 45 ) && ( candy <= 'j' ) ); candy++ ) /* pennies is sentinel variable */
      {
         switch ( candy )
         {
            case 'a' :
               if ( pennies >= 55 )
               {
                  printf( "Mars, " );
                  pennies = pennies - 55;
               }
               break;
            case 'b' :
               if ( pennies >= 55 )
               {
                  printf( "Snickers, " );
                  pennies = pennies - 55;
               }
               break;
            case 'c' :
               if ( pennies >= 55 )
               {
                  printf( "Bounty, " );
                  pennies = pennies - 55;
               }
               break;
            case 'd' :
               if ( pennies >= 85 )
               {
                  printf( "Peanut M&M, " );
                  pennies = pennies - 85;
               }
               break;
            case 'e' :
               if ( pennies >= 85 )
               {
                  printf( "Chocolate M&M, " );
                  pennies = pennies - 85;
               }
               break;
            case 'f' :
               if ( pennies >= 65 )
               {
                  printf( "Aero Bubbles, " );
                  pennies = pennies - 65;
               }
               break;
            case 'g' :
               if ( pennies >= 55 )
               {
                  printf( "Fruit Pastilles, " );
                  pennies = pennies - 55;
               }
               break;
            case 'h' :
               if ( pennies >= 55 )
               {
                  printf( "Wine Gums, " );
                  pennies = pennies - 55;
               }
               break;
            case 'i' :
               if ( pennies >= 45 )
               {
                  printf( "Polo mints, " );
                  pennies = pennies - 45;
               }
               break;
            case 'j' :
               if ( pennies >= 95 )
               {
                  printf( "Haribo Gold Bears " );
                  pennies = pennies - 95;
               }
               break;
         }
      }
      
      money = pennies / 100.0;
      printf( "with change of £%.2f", money );
   }
   else
      printf( "You do not have enough money to buy candy" );
}



Optional challenge problem: Tax calculator


Write a C program that accepts as input a specific amount of income and displays as output total amount of income tax owed to the UK government.

The income tax rates and information are available from the HM Revenue & Customs website:
#include <stdio.h>

int main( void )
{
   double income;
   int pounds;
   
   scanf( "%lf", &income );
   pounds = income; /* downward conversion from floating point to integer whole numbers */

   if ( pounds <= 6035 ) /* personal allowance amount during 2008-09 */
   {
      printf( "You do not owe any taxes" );
      return 1;
   }
   else
      pounds = pounds - 6035;
   
   if ( pounds <= 34800 ) /* income band for 20% basic rate during 2008-09 */
   {
      printf( "You owe £%.2lf of taxes", pounds * 0.20 );
      return 1;
   }
   else
      pounds = pounds - 34800;

   /* 40% higher rate during 2008-09 */
   printf( "You owe £%.2lf of taxes", ( 34800 * 0.20 ) + ( pounds * 0.40 ) );
}



Optional challenge problem: Multiplication tables


Write a C program that uses iterative loops to display multiplication tables from 1 to 10.

Following is a sample output display of multiplication tables for 1 and 2.
1 x 1 = 1
1 x 2 = 2
1 x 3 = 3
1 x 4 = 4
1 x 5 = 5
1 x 6 = 6
1 x 7 = 7
1 x 8 = 8
1 x 9 = 9
1 x 10 = 10
2 x 1 = 2
2 x 2 = 4
2 x 3 = 6
2 x 4 = 8
2 x 5 = 10
2 x 6 = 12
2 x 7 = 14
2 x 8 = 16
2 x 9 = 18
2 x 10 = 20

#include <stdio.h>

int main( void )
{
   int inside, outside;
   
   for ( outside = 1; outside <= 10; outside++ )
   {
      for ( inside = 1; inside <= 10; inside++ )
      {
          printf( "%d x %d = %d \n", outside, inside, outside * inside );
      }
   }
}
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