Thread: syntax confusion with array/pointer

Hello guys -- I have problem. There is specific function within my code that I'm having a hard time reconfiguring. In the "display_temps" function, I want to print a "+" beside the temp if it is higher than the average of the temperatures. I know that it's because of my comparison of the array/pointer with the int variable avg but I don't know what step to take in order to get it to do what I want. can anyone help.

**my code compiles, but only with incorrect results**

Code:

#include <stdio.h>
#include <stdlib.h>


//Function Prototype

void printHeading ();

void input_temps( int temp_array[], int n );

void display_temps( int temps[], int num, int no_of_temps );

void calculate_avg( int temps[], int no_of_temps );



int main()

{
	
	

   int* temps, count;
   int no_of_temps, no_of_bytes;


   
		printHeading ();


	    printf("How many days did you collect temperatures in a month: ");
			
			scanf("%d", &no_of_temps);
	   
		no_of_bytes = no_of_temps*sizeof(int);
	    
		temps = (int*)malloc(no_of_bytes);
		
		

	    
		input_temps(temps, no_of_temps);
		
		calculate_avg(temps, no_of_temps);
		
		display_temps(temps, no_of_temps, no_of_temps);


}


//********************************
// Temp. input function
//********************************


void input_temps(int temp_array[], int n)

{


   int i;
   printf("\n\nEnter the %d temperatures:\n\n", n);
   for (i=1; i<=n; i++)
      scanf("%d", &temp_array[i]);

	  
}


//***************************************
// Display temp. function
//***************************************

void display_temps( int temps[], int num, int no_of_temps )

{


   int i, total;
   int avg;
   
   
   for ( i = 1 ; i <= num ; i++ ) {
      
	//printf("\n\n\t%d \t%d", i , temps[i]);
	 
	 
	 total += temps[i];
	 
	 avg = ( total / no_of_temps );
	 

	if ( avg < temps[i] ) 
	
		printf("\n\n\t%d \t%d +", i, temps[i]);
	
	
		else {
			printf("\n\n\t%d \t%d ", i, temps[i]);

	}
}

}


//***************************************
// Calculate avg. temp
//***************************************

void calculate_avg( int *temps, int no_of_temps)

{

   int i, total;
   float avg;
   total = 0;

 
   for( i = 1; i <= no_of_temps; i++) {
   
      total += temps[i];
}



   avg = ( total / no_of_temps);
   
   

   printf("\nThe average temperature is  %.2f" , avg);
}

You have two major problems with your current code. The first is that your loops are running from 1..n instead of from 0..n-1. In C, array indexes begin at 0 and go to 1 less than the number of elements. Thus, your for loops should look like this:

Code:

for (i = 0; i < num; i++)

The second is that you never initialized total in display_temps, so you're adding the temperatures to some garbage value that's hanging around on the stack. Regardless of this second problem, I strongly suggest you take Tater's advice and have calculate_average return the average value and pass that in to your display_temps function, which doesn't need both num and no_of_temps, since they're the same.

@commontater I tried returning avg and passing it as a parameter but it didn't work -- I'll try something else.

Or post your new code and we will help you track down your problems with Tater's suggestion (which is much better from a design standpoint).

As an amendment to my previous post, even if you do initialize total, your average in display_temps isn't correct. When i is 0, you have only 1 element in your total, but you divide it by the number of total temperatures. Let's say there were the following 5 temps: 10, 20, 30, 40, 50. Your average on the first iteration would be 10/5 = 2. The second iteration would be (10+20)/5 = 6, and so on. The "average" would be changing each time and would only be correct on the last iteration, but at that point it's too late.

@anduril462 I see what you're saying about the first part but I chose to do that so when I print out my input it will show 1 first, not 0. Secondly, I tried passing "return avg;" from calculate_avg and I got nothing but errors saying return with a value in function returning void.

Here is the revised code

Code:

//Function Prototype

void printHeading ();

void input_temps( int temp_array[], int n );

void display_temps( int temps[], int num, float avg);

void calculate_avg( int temps[], int no_of_temps );



int main()

{
	
	

   int* temps, count;
   int no_of_temps, no_of_bytes;


   
		printHeading ();


	    printf("How many days did you collect temperatures in a month: ");
			
			scanf("%d", &no_of_temps);
	   
		no_of_bytes = no_of_temps*sizeof(int);
	    
		temps = (int*)malloc(no_of_bytes);
		
		

	    
		input_temps(temps, no_of_temps);
		
		calculate_avg(temps, no_of_temps);
		
		display_temps(temps, no_of_temps, avg);


}


//********************************
// Temp. input function
//********************************


void input_temps(int temp_array[], int n)

{


   int i;
   printf("\n\nEnter the %d temperatures:\n\n", n);
   for (i=1; i<=n; i++)
      scanf("%d", &temp_array[i]);

	  
}


//***************************************
// Display temp. function
//***************************************

void display_temps( int temps[], int num, float avg)

{


   int i;
   
   
   for ( i = 1 ; i <= num ; i++ ) {
      
	printf("\n\n\t%d \t%d", i , temps[i]);
	
	 
	 
	 //total += temps[i];
	 
	 //avg = ( total / no_of_temps );
	 

	
	
		//printf("\n\n\t%d \t%d +", i, temps[i]);
	
	
		//else {
			//printf("\n\n\t%d \t%d ", i, temps[i]);

	
}
printf("%.2f", avg);
}


//***************************************
// Calculate avg. temp
//***************************************

void calculate_avg( int *temps, int no_of_temps)

{

   int i, total;
   float avg;
   total = 0;

 
   for( i = 1; i <= no_of_temps; i++) {
   
      total += temps[i];
}



   avg = ( total / no_of_temps);
   
   

   printf("\nThe average temperature is  %.2f" , avg);
   
   return( avg);

}

I tried passing "return avg;" from calculate_avg and I got nothing but errors saying return with a value in function returning void.

This is the compiler telling you you're not doing something correctly. Listen to it and learn. If you read it carefully, it says you are returning a value in a function that is declared to return void, or nothing. You need to tell the compiler your function should return a float value, by declaring it like this:

Code:

float calculate_avg( int *temps, int no_of_temps)

. Then you can safely use "return avg;".

I chose to do that so when I print out my input it will show 1 first, not 0.

That's nice and all, but it's just plain wrong. I told you that in my previous post, and said it was a "major problem", not a suggestion. You can't just have C change the way it indexes arrays, it's from 0..n-1. If you want to print output starting at 1, you're just going to have to deal with writing something like "printf("%d", i+1)" all over. As is, you have basically written buffer overflows into your program simply for output aesthetics. This may not seem like an issue now, but as your programs grow in complexity, you will find yourself tromping all over other values and causing nightmarish problems to debug.

Now, with your latest version, there are still a few kinks to work out:
1. As I mentioned above, you need to change calculate_avg to have a return type of float.
2. You need to fix your array indexes as I mentioned in my previous post. Adjust your output as necessary.
3. You declared main to return an int, but there is no return statement in there. Finish the function with a "return 0;".
4. You need to declare a float variable in main called avg, and assign it the return value of calculate_avg, like so:

Code:

float avg;
...
avg = calculate_avg(...);

thanks anduril, I appreciate it