Thread: Help with max value of an array

Hi, my program needs to return the max value of an array given the input of the user. I believe I am pretty close to getting it to work, but I know I have a few errors. Calling functions still confuses me and I think that is where I am going wrong.

Here is my code:

Code:

#include<stdio.h>

int findLargest(double *array, int arrayLength);

int main()
{
 double nums[80];
 int pos;

   for (pos=0; pos<10 && nums[pos]!=EOF; ++pos)
   {
    printf("Enter in a number or EOF to quit: ");
    scanf("%lf", &nums[pos]);
   }

   for (pos=0; pos<10; ++pos)
   {
   printf("%lf\n", nums[pos]);
   }
   
 double maximum = findLargest(nums, pos);
 int OS;
 
    if(pos<=0)
	printf("There is no maximum element,\n");
	else
    printf("The maximum value is %lf at offset %d\n", maximum, OS); 
}

int findLargest(double *array, int arrayLength)
{
   if (arrayLength <= 0)
   {
   return -1;
   }
   
 int offset=0;
 int i;
 double max = array[0];
 
   for (i=0; i<arrayLength; ++i)
   {
      if (max < array[i])
	  {
	   max=array[1];
	  }
   }
 
 return max;
}

Any help or suggestions would be greatly appreciated!!

What about functions do you not understand?

1. nums[pos] will never equal EOF - you don't scanf() until inside the for() loop.
2. never check for programmer error ... if (arrayLength <= 0). name one C function that attempts to protect you against your own bad programming.
3. why would you return -1 to be stored as maximum value? that is not logical. AND you already checked if(pos <= 0).
4. you never use variable offset in findLargest()
5. you never assign a value to variable OS.

I just get confused with exactly how to get what I want out of the function.

Okay so I have fixed up most of what I need, the only part I really don't get right now is how to use pointers properly here. I need to get the values for both max and offset from my function into main and print them in my printf statement. How do I do this?


This is my newer code:

Code:

#include<stdio.h>

int findLargest(double *array, int arrayLength);

int main()
{
 double nums[80];
 int pos;
 

   for (pos=0; pos<10; ++pos)
   {
    printf("Enter in a number or EOF to quit: ");
    if(scanf("%lf", &nums[pos])<=0)
	  break;
   }

 double maximum = findLargest(nums, pos);
 
    if(pos<=0)
   	  printf("There is no maximum element.\n");
	else
      printf("The maximum value is %lf at offset %d\n", maximum, pos); 
}

int findLargest(double *array, int arrayLength)
{
   if (arrayLength <= 0)
     return -1;
   
 int offset=0;
 int i;
 double max = array[0];
 
   for (i=0; i<arrayLength; ++i)
   {
      if (max < array[i])
	    max=array[i];
		offset=i;
   }
 
 return offset;
}

A function can only return one value. If you need more than that from a function, you need to use pass by reference, and give the function variable addresses as parameters where you want the function to change a value for you. You then need to use indirection or de-referencing to affect the change.

Code:

void changeMyVars( int [], int len, char *middle) ;

int main( void )
{
    int arr[] = "Hello World" ;
    char letter = ' ' ;

    changeMyVars( arr, strlen(arr), &letter ) ;  // passing the address of letter to the function
//...
}

void changeMyVars( int a[], int len, char *mid )  // variable pointer mid gets the address of letter as it's value
{
     len /= 2 ;

     *mid = a[len] ;  //indirection assigns the value of a[len] to the address of letter
}

Cheesy little code to show how a function can directly change a variable that isn't in it's own scope. Hope the example helps.