Iterate variable (newbie)

This is a discussion on Iterate variable (newbie) within the C Programming forums, part of the General Programming Boards category; Just starting C, so I have some problems with the basics! I have several inputs and need to identify the ...

  1. #1
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    Post Iterate variable (newbie)

    Just starting C, so I have some problems with the basics!

    I have several inputs and need to identify the largest inputted number.
    I am told by my teacher to use a loop.

    so far I have this
    Code:
                    float n1, n2;
    
    	while (n1 >= 0)
    	{
    		printf("Enter any number: \n");
    		scanf("%f", &n1);
    		printf("Enter any number: \n");
    		scanf("%f", &n2);
    		/* Reads two numbers */
    		if (n1 > n2)
    			max = n1;
    		else
    			max = n2;
    		/* Compare the two numbers, keep the higher number. */
    	}
    	printf("Largest number is: %f", max);
    I want the program to stop running and outputting the highest number if 0 or a negative number is inputted.
    I see the potential bug with n1 >= 0 with that n2 can be typed in as a break parameter.

    Should I possibly pull the n1, n2 outside the while loop and then keep the 'max' inside the loop ?

  2. #2
    Registered User C_ntua's Avatar
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    If you want to end the loop if n2 is also >= 0 you will do:
    Code:
    while (n1>=0 && n2>=0) {
      ...
    }
    And you HAVE to initialize n1 (and n2 if you use the above code). If you don't it will automatically initialized, so it might be <0 in the begining. You should do:
    Code:
    float n1=1, n2;

  3. #3
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    Thanks C_ntua

    I continued work, and I think I have simplified it a bit:

    Code:
    int main(void) {
    	float n1, max=0;
    
    	while (n1 > 0)
    	{
    		printf("Enter any number: ");
    		fflush(stdout); /* Compiler won't stop to print line */
    		scanf("%f", &n1);
    		
    		if (n1 > max)
    			max = n1;
    	}		
    
    	printf("Largest number is: %f", max);
    
    	return EXIT_SUCCESS;
    But now it won't stop t ask me for a input?

  4. #4
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    I don't want to initialize n1 since it can be any positive number and I risk initializing it higher than the inputted number.

    Code:
    int main(void) {
    	float n1, max=0;
    	
                    printf("Enter any number: ");
    	fflush(stdout);
    	scanf("&#37;f", &n1);
    
    	/* Putting the input outside the loop, I make sure n1 is never 
    	 * a random number and will always continue to the while loop*/
    	
    	while (n1 > 0)
    	{
    		printf("Enter any number: ");
    		fflush(stdout); /* Compiler won't stop to print line */
    		scanf("%f", &n1);
    		
    		if (n1 > max)
    			max = n1;
    	}		
    
    	printf("Largest number is: %f", max);
    
    	return EXIT_SUCCESS;
    I put another line outside the loop, but I think it looks a bit untidy... is there any way of simplifying this, so I don't have repeating-lines?

    edit: Oddly, it reads the decimal numbers as the highest numbers, if I type number like 25 and 0.25 it will read out the 0.25 as the higher number. If I only use integers, it works as intended?
    Last edited by Roffemuffe; 10-15-2008 at 07:17 AM.

  5. #5
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    You could initialise max to the same as the first number entered, and then at the end test to see if max is <= 0. If so, output a message saying that no numbers were input instead of the highest number.

    A variable must always have a known value before you test it .... attempting to test an undefined variable is asking for undefined behaviour

  6. #6
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    The part outside the while loop isn't used. As far as I can see, it reads a number, then goes to while-loop, reads a new number and works on that number, but forgets to work on the first number I typed in.

    I added a line to max = n1 and now is working as intended, thanks Driver!

    Code:
    int main(void)
    {
          int n1, max=0;
          printf("Enter any number (0 to end): ");
          fflush(stdout);
          scanf("%f", &n1);
    ->    max = n1;
    
    while ...

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