1 reply to this topic

[johnobri]

Hi all

This is a simple program in C for taking in a person's choice of lotto numbers, asking them if they want to change their mind and if not printing them to the screen. It works but to get it to work, on the line marked * I had to increment the dummy variable "index" by 6. I would have thought by 1 would be sufficent. I seems by the time the program has got to line * the index has been zeroed. How has it been zeroed?
Again to reiterate it works as shown below but why must index be increment ed by 6/ why/how has the index been zeroed by line * ?

Thank you

# include<stdio.h>
main()
{

// DECLARE ARRAY WITH 6 ELEMENTS
  int numb[5];

// DECLARE VARIABLES

/* 'Index' IS USED FOR COUNTING THROUGH THE ARRAY AND FOR
PRINTING “ENTER NUMBER 1”, “ENTER NUMBER 2” ETC. */
  int index;

// CH IS USED FOR ACCEPTING ‘Y’ OR ‘N’ FROM USER
  char ch;

  printf("\n\t\t\t The National Lottery\n\n");
  printf("\n\t\t\t You could be a winner \n\n");

// DO LOOP FOR TAKING IN 6 NUMBERS FROM THE USER WHILE INDEX IS <=5.
  do
  {
    printf("Please choose your six numbers (0 - 60)\n\n");

// BEGINNING AT 0; CONTINUE WHILE INDEX IS <=5;INCREMENT
// INDEX BY 1 EACH TIME THROUGH THE LOOP IF ALL IS OK
for (index=0; index<=5; index=index+1)
      {

/* INDEX+1 BECAUSE INDEX IS AT 0 (FOR ENTERING INTO THE ARRAY) BUT INDEX IS
ALSO USED TO ASK THE USER TO “ENTER NUMBER ?” SO IT SHOULD BE AT 1 SO THAT
“ENTER NUMBER 1” IS PRINTED, NEXT TIME THROUGH THE LOOP IT WILL PRINT “ENTER
NUMBER 2” THE CODE “INDEX + 1” ACHIEVES THIS.*/
	printf("Enter number %d : ", index+1);

// SCAN IN THE NUMBER AND PUT IT IN THE ARRAY (INDEX IS CURRENTLY AT 0)
	scanf("%d", &numb[index]);

/*WHEN THE USER ENTERS A NUMBER WHICH IS NOT BETWEEN 1-60, ASK THEM TO RE-ENTER */
	if(numb[index]<1 || numb[index]>60)
	{
	  printf("Please re-enter number %d (between 0 - 60)!!!\n", index+1);
	  index=index-1;
	}
      }
/*ASK THE USER IF THEY WANT TO ENTER 6 DIFFERENT LOTTO NUMBERS AGAIN, OR NOT*/
    printf("\nDo you wish to enter six different lotto numbers [Y/N] ? ");

// SCAN THE USER'S REPLY, ENSURINGNO WHITESPACE CHARACTERS ARE ACCEPTED ("%LS")
// AND PUT THE ENTRY IN CH
    scanf("%ls",&ch);

// USER WANTS 6 NEW NUMBERS
    if (ch == 'y' || ch == 'Y')
    {
      index=0;
      printf("\n");
    }

// USER WANTS TO STICK WITH THEIR 6 NUMBERS
    else if (ch == 'n' || ch == 'N')	/*IF THE ENTER IS N, EXIT THE PROGRAM*/
    {

// HERE IS WHERE INDEX IS INCREMENTED, FOR ADDING TO THE ARRAY AND PRINTING
// “Enter number 1, Enter number 2, Enter number 3 etc”
      index=index+6; *
      printf("\n");

// MEANS THAT WE LEAVE THE MAIN DO LOOP AND PRINT THE ENTERED NUMBERS (UNDER THE LOOP)
    }

// WRONG ENTRY BY THE USER
    else
    {

// PUT INDEX TO 0 AND START AGAIN AT THE BEGINNING OF THE LOOP
      index=0;
      printf("\nYour entry must be 'Y' or 'N'. ");
      printf("\nPlease re-enter your numbers.\n\n");
    }
  }
  while(index<=5);

/*OUTPUT THE SIX FINAL NUMBERS*/
  printf("\nThe six lotto numbers you have chosen are :");
  printf("\n%5d %5d %5d %5d %5d %5d", numb[0],numb[1],numb[2],numb[3],numb[4],numb[5]);		}

Edited by WingedPanther, 30 April 2009 - 07:10 AM.
add code tags (the # button)

[WingedPanther]

First observation:
your code is grossly over-commented and your indentation is completely scrambled. Reading your code is very painful. The variety of comment styles didn't help either.

I think your bug is an obscure one: you declared numb as an array of FIVE ints, not six. The result is that numb[5] is outside the array and likely over-writing index (which would naturally be allocated at memory location numb[5]).

Finally, your do/while loop exit condition is not based on what you really want. You want to loop when ch != 'y' and ch != 'Y'.

# include<stdio.h>
main()
{

  // DECLARE ARRAY WITH 6 ELEMENTS
  int numb[6]; //This needs to be a 6 if you want six elements.  

  // DECLARE VARIABLES

  // 'Index' IS USED FOR COUNTING THROUGH THE ARRAY AND FOR
  // PRINTING “ENTER NUMBER 1”, “ENTER NUMBER 2” ETC. 
  int index;

  // CH IS USED FOR ACCEPTING ‘Y’ OR ‘N’ FROM USER
  char ch;

  printf("\n\t\t\t The National Lottery\n\n");
  printf("\n\t\t\t You could be a winner \n\n");

  // DO LOOP FOR TAKING IN 6 NUMBERS FROM THE USER WHILE INDEX IS <=5.
  do
  {
    printf("Please choose your six numbers (0 - 60)\n\n");

    for (index=0; index<=5; index=index+1)
    {

      // INDEX+1 BECAUSE INDEX IS AT 0 (FOR ENTERING INTO THE ARRAY) BUT INDEX IS
      // ALSO USED TO ASK THE USER TO “ENTER NUMBER ?” SO IT SHOULD BE AT 1 SO THAT
      // “ENTER NUMBER 1” IS PRINTED, NEXT TIME THROUGH THE LOOP IT WILL PRINT “ENTER
      // NUMBER 2” THE CODE “INDEX + 1” ACHIEVES THIS.
      printf("Enter number %d : ", index+1);

      // SCAN IN THE NUMBER AND PUT IT IN THE ARRAY (INDEX IS CURRENTLY AT 0)
      scanf("%d", &numb[index]);

      // WHEN THE USER ENTERS A NUMBER WHICH IS NOT BETWEEN 1-60, ASK THEM TO RE-ENTER 
      if(numb[index]<1 || numb[index]>60)
      {
        printf("Please re-enter number %d (between 0 - 60)!!!\n", index+1);
        index=index-1;
      }
    }
    // ASK THE USER IF THEY WANT TO ENTER 6 DIFFERENT LOTTO NUMBERS AGAIN, OR NOT
    printf("\nDo you wish to enter six different lotto numbers [Y/N] ? ");

    // SCAN THE USER'S REPLY, ENSURINGNO WHITESPACE CHARACTERS ARE ACCEPTED ("%LS")
    // AND PUT THE ENTRY IN CH
    scanf("%ls",&ch);

    // VALID EXIT CODE
    if (ch == 'y' || ch == 'Y' || ch == 'n' || ch == 'N')
    {
      printf("\n");
    }
    // WRONG ENTRY BY THE USER
    else
    {
      printf("\nYour entry must be 'Y' or 'N'. ");
      printf("\nPlease re-enter your numbers.\n\n");
    }
  } while(ch != 'y' && ch != 'Y');

  // OUTPUT THE SIX FINAL NUMBERS
  printf("\nThe six lotto numbers you have chosen are :");
  printf("\n%5d %5d %5d %5d %5d %5d", numb[0],numb[1],numb[2],numb[3],numb[4],numb[5]);	
}