Measurement with structure and searching for least, largest and average temperature - c

Question

I have to write a program for recording the measured temperatures,
into which new measurements can be entered, or display statistics calculated from previous measurements. In the case of printing statistics, it is necessary to find and display the lowest and highest recorded temperature and calculate the average temperature.
#include <stdio.h>
int least_in_array(int array[], int n)
{
int i, least=array[0];
for(i=0; i<n; i++)
{
if(array[i]<least)
{
least=array[i];
}
}
return least;
}
int largest_in_array (int array[], int n)
{
int i, largest=array[0];
for(i=0; i<n; i++)
{
if(array[i]>largest)
{
largest=array[i];
}
}
return largest;
}
float average_array(int array[], int n)
{
int amount=0, i;
for(i=0; i<n; i++)
{
amount+=array[i];
}
return (1.0*amount)/n;
}
int main() {
int choose;
struct Data1 {
int dayInMonth;
int month;
float temperature;
} da;
printf("New measurement(1) or statistic(2)?\n");
scanf("%d", &choose);
if(choose==1) {
printf("Enter the day in month : ");
scanf("%d", &da.dayInMonth);
printf("Enter month : ");
scanf("%d", &da.month);
printf("Enter temperature (*C) : ");
scanf("%f", &da.temperature);
printf("Data saved!");
printf("-----------\n");
return 0;
}
if(choose==2) {
//printf("Least temperatures in quarter: %d", least_in_array(dayInMonth) );
return 0;
}
else {
printf("----------------\n");
printf("Wrong choose!\n");
}
return 0;
}
In case 2, I commented line where I get an error. Can anyone give me any advice to fix this problem?
|71|error: 'dayInMonth' undeclared (first use in this function)
|71|error: too few arguments to function 'least_in_array'

Answer 1

Since it is Christmas Eve, lets help out fellow man... who obviously is badly in need. For code that is supposed to pass an array to least_in_array, largest_in_array and average_array -- you have no array! That somewhat puts you behind the eight-ball from the word "Go!".
Your thought to use a stuct to capture and coordinate dayInMonth, month and temperature is 100% correct. (but note: C-style generally avoids camelCase variable names in favor of all lowercase). Also, defining struct Data1 within main() prevents your functions above that point from knowing what struct Data1 is, so you need to move your struct definition to the top of the file. (or provide a forward declaration, but we will save that for later) For now, let's just move your Data1 to the top (I used a typedef to alleviate having to prefix each use with stuct and renamed Data1 data:
#define NDAYS 365
typedef struct {
int day,
month;
double temperature;
} data;
Note the defined constant NDAYS. Since you are going to need an array, and since a dynamically allocated and reallocated approach seem well beyond your needs here, let's just define a constant, a maximum, for the number of elements we will have in our array.
Now, before we go further, let's think about our array. If we are going to use a struct to hold the associated date and temperature measurement, then we are going to need an array of... what?? An array of struct. And with our constant NDAYS, we will declare a maximum of 365 elements in our array. So how would this work? We have our stuct typedeffed to data, so if we want an array of data we need:
data da[NDAYS] = {{0, 0, 0.0}};
Note: the older initializer format initializing each field was used as it is unclear whether you could be using a C89 compiler. C99 and later added named initializers , e.g. {{.day = 0}} and any uninitialized elements are implicitly initialized to zero.
Now we have an array of data and can capture measurements. Of course you are responsible for keeping track of the indexes you fill. A simple counter, incremented each time a successful measurement in entered is all you need (ndx is used below)
How do we make least_in_array, largest_in_array and average_array work with an array of data? Recall, we moved the definition of the struct to the beginning of the source file, so now each function knows what data is. We simply need to pass our array of data as a parameter, e.g.
float least_in_array (data *array, int n)
{
int i;
float least = INT_MAX; /* sufficiently high temp */
for (i = 0; i < n; i++)
if (array[i].temperature < least)
least = array[i].temperature;
return least;
}
(note, each of the quantities of least_in_array, largest_in_array and average_array refer to the temperature values and therefore need to return type float.)
The remainder of putting together largest_in_array and average_array follows the same pattern.
The crux of your remaining problems relate to handling user input, and the particular pitfalls associated with taking user input with scanf. It can be done, but you must always validate the return, and test for user cancellation of input by testing for EOF (the result of the user pressing Ctrl+d (or Ctrl+z on windoze)).
You must validate that the number of expected conversions did in fact take place, or you must handle the error, and most importantly, you must account for any characters left in the input buffer (e.g. stdin), otherwise, if an invalid entry is made and you don't remove it from stdin, you will loop forever... (with scanf if a matching or input failure occurs -- no additional character are processed -- leaving them where? (oh, in stdin)
You can make this fairly easy on yourself if you declare a few helper functions to empty stdin, and make the normal process of getting an integer or float from the user relatively safe. For example, to empty stdin, you simply read all remaining characters until a '\n' or EOF is encountered, e.g.
/** simple function to empty all characters that remain
* in stdin. Needed when using scanf for user input.
*/
void empty_stdin()
{
int c = getchar();
while (c != '\n' && c != EOF)
c = getchar();
}
To ask the user for an int or float, you simply validate the return, check the number of successful conversion (what scanf returns), check whether EOF was generated by the user, and finally handle the error if invalid input was given and empty_stdin as required. You generally want to loop until the user either provides valid input, or cancels. (an invalid input does you no good).
For example, getting integer input can be handled as follows. (note: I put it in a function to keep from repeating this block of code for each input you take in the main body of your code...
/** abbreviated function to read integer value from user.
* returns value on success, exits if user cancels.
* empties stdin after call to scanf.
*/
int getint ()
{
int n = 0;
for (;;) { /* loop until valid input or EOF */
int rtn = 0; /* variable to capture return of scanf */
rtn = scanf ("%d", &n);
if (rtn == 1) { /* we got an integer */
empty_stdin();
break;
}
else if (rtn == EOF) { /* if user cancels, exit */
fprintf (stderr, "user canceled input.\n");
exit (EXIT_FAILURE);
}
if (rtn == 0) /* handle error */
fprintf (stderr, "getint() error: invalid integer input.\n");
empty_stdin(); /* empty all chars remaining in stdin */
}
return n;
}
(taking input for a float works the same way).
Lastly, you generally want to avoid using float in most cases, using double instead, just due to loss of precision and limitations for representing floating-point numbers with a 23-bit mantissa. However, here we are taking temperature, and float will suffice for this code.
Putting it altogether, you could do something like the following. Note, I have left your functions before main() as you had them, and added the helper function definitions after main(), but provided declarations before main() so they are visible to main() :
#include <stdio.h>
#include <stdlib.h>
#include <limits.h>
#define NDAYS 365
typedef struct {
int day,
month;
double temperature;
} data;
float least_in_array (data *array, int n)
{
int i;
float least = INT_MAX; /* sufficiently high temp */
for (i = 0; i < n; i++)
if (array[i].temperature < least)
least = array[i].temperature;
return least;
}
float largest_in_array (data *array, int n)
{
int i;
float largest = INT_MIN; /* sufficiently low temp */
for (i = 0; i < n; i++)
if (array[i].temperature > largest)
largest = array[i].temperature;
return largest;
}
float average_array (data *array, int n)
{
int i;
float sum = 0.0;
for (i = 0; i < n; i++)
sum += array[i].temperature;
return sum / (float)n;
}
void empty_stdin();
int getint();
float getfloat();
int main (void) {
int ndx = 0;
float max = 0.0, min = 0.0, avg = 0.0;
data da[NDAYS] = {{0, 0, 0.0}};
for (;;) {
int choose = 0;
printf ("\n (1) New measurement\n"
" (2) Statistics\n"
" (3) Exit\n\n"
" choice: ");
choose = getint();
putchar ('\n');
switch (choose) {
case 1: if (ndx == NDAYS) {
fprintf (stderr, "error: array full.\n");
break;
}
printf (" Enter day in month : ");
da[ndx].day = getint();
printf (" Enter month : ");
da[ndx].month = getint();
printf (" Enter temperature : ");
da[ndx].temperature = getfloat();
printf (" da[%3d] saved\n"
" ----------------------------\n", ndx++);
break;
case 2: if (ndx == 0) {
fprintf (stderr, "error: no measurements taken.\n");
break;
}
min = least_in_array (da, ndx);
max = largest_in_array (da, ndx);
avg = average_array (da, ndx);
printf (" minimum temp : %.2f\n"
" maximum temp : %.2f\n"
" average temp : %.2f\n"
" ----------------------------\n",
min, max, avg);
break;
case 3:
goto done;
break;
default:
fprintf (stderr, "error: invalid choice.\n");
empty_stdin();
break;
}
}
done:;
return 0;
}
/** simple function to empty all characters that remain
* in stdin. Needed when using scanf for user input.
*/
void empty_stdin()
{
int c = getchar();
while (c != '\n' && c != EOF)
c = getchar();
}
/** abbreviated function to read integer value from user.
* returns value on success, exits if user cancels.
* empties stdin after call to scanf.
*/
int getint ()
{
int n = 0;
for (;;) { /* loop until valid input or EOF */
int rtn = 0; /* variable to capture return of scanf */
rtn = scanf ("%d", &n);
if (rtn == 1) { /* we got an integer */
empty_stdin();
break;
}
else if (rtn == EOF) { /* if user cancels, exit */
fprintf (stderr, "user canceled input.\n");
exit (EXIT_FAILURE);
}
if (rtn == 0) /* handle error */
fprintf (stderr, "getint() error: invalid integer input.\n");
empty_stdin(); /* empty all chars remaining in stdin */
}
return n;
}
/** abbreviated function to read float value from user.
* returns value on success, exits if user cancels.
* empties stdin after call to scanf.
*/
float getfloat ()
{
float v = 0.0;
for (;;) { /* loop until valid input or EOF */
int rtn = 0; /* variable to capture return of scanf */
rtn = scanf ("%f", &v);
if (rtn == 1) { /* we got an float */
empty_stdin();
break;
}
else if (rtn == EOF) { /* if user cancels, exit */
fprintf (stderr, "user canceled input.\n");
exit (EXIT_FAILURE);
}
if (rtn == 0) /* handle error */
fprintf (stderr, "getint() error: invalid float input.\n");
empty_stdin(); /* empty all chars remaining in stdin */
}
return v;
}
Note: how the array bounds are limited to 365 or less in your take measurement part of the code, and how a check is made that there is at least one measurement present before any statistics can be provided. You always need to validate each step of the process. Look for corner-cases, think about what could go wrong with input (what if a cat stepped on the keyboard), and then go provide validations and checks to handle each case. The validations above are just the bare minimum, there are always more you can add to more fully report and handle each error condition.
Example Use/Output
$ ./bin/tempmxmnavg
(1) New measurement
(2) Statistics
(3) Exit
choice: 2
error: no measurements taken.
(1) New measurement
(2) Statistics
(3) Exit
choice: 1
Enter day in month : 8
Enter month : 2
Enter temperature : 20.0
da[ 0] saved
----------------------------
(1) New measurement
(2) Statistics
(3) Exit
choice: 1
Enter day in month : 9
Enter month : 2
Enter temperature : 30.0
da[ 1] saved
----------------------------
(1) New measurement
(2) Statistics
(3) Exit
choice: 1
Enter day in month : 10
Enter month : 2
Enter temperature : 70.0
da[ 2] saved
----------------------------
(1) New measurement
(2) Statistics
(3) Exit
choice: 2
minimum temp : 20.00
maximum temp : 70.00
average temp : 40.00
----------------------------
(1) New measurement
(2) Statistics
(3) Exit
choice: 3
Look things over and let me know if you have any further questions (although given the evening, I won't be here much longer...)