Passing struct array to function and calculating average in C? - c

Question

Beginner here, I've been trying this for hours and can't get it to work, searched online too and couldn't find an answer.
I'm trying to write a program where you input people by putting their age and height then calculate the average of each, and the average ratio of age to height. Whenever I pass the struct to my getAverage function, it returns the address (I think) instead of the averages.
#include <stdio.h>
#include <stdlib.h>
typedef struct person
{
int age;
double height;
} Person;
double getAv (Person people[50], int max)
{
int i;
double total, retval;
total = 0;
for (i=0; i<=max; i++)
{
total = total + people[i].age;
}
retval = total / max;
return retval;
}
int main (void)
{
Person people[50];
int i;
while (i++, people[i].age>=0)
{
printf ("Person #%d\n", i);
printf ("enter an age: ");
scanf ("%d", &people[i].age);
if (people[i].age<0)
break;
printf ("enter a height: ");
scanf ("%lf", &people[i].height);
printf ("\n");
}
double averageAge;
averageAge = getAv (&people[50], i);
printf ("%.1lf\n", averageAge);
}
Haven't implemented average height or ratio yet, just trying to get average of ages to work for now. When I try taking the & out of averageAge = getAv(&people[50], I); I get a compile error that tells me it needs the &. Any help would be appreciated.

Answer 1

There are serveral issues in you code, the first one:
Person people[50];
int i;
while (i++, people[i].age>=0)
You are using i uninitialized, thus, incrementing a variable containing garbage (or 0 as intended, but it is impossible to guarantee)
To avoid such problems in the future enable warnings on your compiler, the compiler would have told you something like:
‘i’ is used uninitialized in this function [-Wuninitialized]
So switch to
Person people[50] = {0};
int i = 0;
It seems (based on the pre-increment operator ++i) that you want to use arrays with base 1, there is nothing wrong with that, but in your average function you are starting from 0, so use a for:
for (i = 0; ; i++)
{
...
if (people[i].age <= 0) break;
...
}
Another issue:
double averageAge;
averageAge = getAv (&people[50], i);
In this way you are passing only element 50 which is not part of your array (remember arrays are base 0 in C), to pass the entire array:
averageAge = getAv (people, i);
or
averageAge = getAv (&people[0], i);
The last one:
for (i=0; i<=max; i++)
You are including the element discarded when you was checking for age > 0, switch to:
for (i=0; i<max; i++)
A minor issue:
Iif the user enters 0 for the first element of people you end up dividing by 0
double averageAge;
averageAge = getAv (&people[50], i);
printf ("%.1lf\n", averageAge);
should be
if (i > 0)
{
double averageAge;
averageAge = getAv (people, i);
printf ("%.1f\n", averageAge); // No need to use lf (long double)
}

Answer 2

If you do it this way, you need to receive in your function (Person& people[], int n)
Where n is the length of the array.
We use the '&' to not do copies of the array and also you are passing only the element with index 50 in the function, simply do only (people, n)

Answer 3

there are mistakes in this code ,first you should initialize int i to int i=0 in mian function.
how are using this condition while (i++, people[i].age>=0) when you haven't scanned any input it's like using an uninitialized variable. you need a do-while like this
do
{
printf("Person #%d\n", i);
printf("enter an age: ");
scanf("%d", &people[i].age);
if (people[i].age < 0)
break;
printf("enter a height: ");
scanf("%lf", &people[i].height);
printf("\n");
i++;
} while (people[i-1].age >= 0);
also you are sending wrong arguments to your getAv function you should use averageAge = getAv (people, i);.
and in your function you have to remove = in this loop for (i=0; i<=max; i++) .this should be for (i=0; i<max; i++) ,otherwise the negative entered age will also be add to total and will affect the average.