Need help understanding logic of function - c

Question

monthly->maxTemperature = yearData[i].high;
monthly->minTemperature = yearData[i].low;
I just can't seem to understand the logic of what the iterations will look like or how to access the proper elements in the array of data to get the proper data for each month.... without corrupting data. Thanks!

Answer 1

You're on the right track:
void stats(int mth, const struct Data yearData[], int size, struct Monthly* monthStats)
{
// These are used to calc averages
int highSum = 0;
int lowSum = 0;
int days = 0;
// Initialize data
monthly->maxTemperature = INT_MIN;
monthly->minTemperature = INT_MAX;
monthly->totalPrecip = 0;
for (int i = 0; i < size; ++i) {
// Only use data from given month
if (yearData[i].month == mth) {
days += 1;
if (yearData[i].high > monthly->maxTemperature) monthly->maxTemperature = yearData[i].high;
if (yearData[i].low < monthly->minTemperature) monthly->minTemperature = yearData[i].low;
highSum += yearData[i].high;
lowSum + yearData[i].low;
monthly->totalPrecip += yearData[i].precip;
}
}
if (0 != days) {
monthly->avgHigh = highSum / days;
monthly->avgLow = lowSum / days;
}
}

Answer 2

Before working on the assignment it's a good idea to examine the API that you need to implement for clues. First thing to notice is that the reason the struct Monthly is passed to your function by pointer is so that you could set the result into it. This is different from the reason for passing struct Data as a pointer*, which is to pass an array using the only mechanism for passing arrays available in C. const qualifier is a strong indication that you must not be trying to modify anything off of the yearData, only the monthStats.
This tells you what to do with the min, max, average, and total that you are going to find in your function: these need to be assigned to fields of monthStats, like this:
monthStats->maxTemperature = maxTemperature;
monthStats->minTemperature = minTemperature;
...
where maxTemperature, minTemperature, and so on are local variables that you declare before entering the for loop.
As far as the for loop goes, your problem is that you ignore the mth variable completely. You need to use its value to decide if an element of yearData should be considered for your computations or not. The simplest way is to add an if to your for loop:
int maxTemperature = INT_MIN; // you need to include <limits.h>
int minTemperature = INT_MAX; // to get definitions of INT_MIN and INT_MAX
for(int i = 0; i<size; ++i) {
if (yearData[i].month < mth) continue;
if (yearData[i].month > mth) break;
... // Do your computations here
}
* Even though it looks like an array, it is still passed as a pointer