C programming, doing multiple calculations in one function

Question

Is it possible to create a function and do multiple calculations in that function, then create another function to print out the results of the calculations... I know a function can only return one value.

You can set multiple values by passing pointer arguments to be set by the function. Or you can define a `struct` which contains all the results, and return that as the function value. — Weather Vane, May 29 '17 at 20:01
You want to check one of these paper-thingies: https://stackoverflow.com/questions/562303/the-definitive-c-book-guide-and-list — too honest for this site, May 29 '17 at 20:22

Stewart · Answer 1 · 2017-05-29T20:29:51.680

4

There are several ways to return multiple values. One way is to "package" them as a struct:

typedef struct
{
  int x;
  float y;
} Result;

Result add2( int x1, int x2, float y1, float y2)
{
  Result r;
  r.x = x1 + x2;
  r.y = y1 + y2;
  return r;
}

Another way to do it is to use parameters as your outputs:

void add2( int x1, int x2, float y1, float y2, int* x, float* y)
{
  *x = x1 + x2;
  *y = y1 + y2;
}

You could also do combinations of these.

edited May 29 '17 at 20:29

answered May 29 '17 at 20:07

Stewart

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You need a `typedef` in order to use `Result` without the `struct` keyword. – David Ranieri May 29 '17 at 20:13
That's a good example, but when all the fields in the `struct` are of the same type, you could achieve the same by using an array. A better example (more general one) is if they were of different types. – SHG May 29 '17 at 20:13
@SHG: Just because you *can* achieve the same result with an array, doesn't mean it's preferable to. A two-dimensional coordinate value, for example, would be better represented as a `struct` than as a two-element array. And obviously you can't return an array from a function, so if you wanted to do this, you'd still need to wrap it in a `struct`. – Crowman May 29 '17 at 20:17
@PaulGriffiths Right. I didn't say it's preferable, just that you can. And if you show an example for a concept, make it general. Obviously one of the advantages of a struct would be to be able to return different types, so it's better to be demonstrated as well. – SHG May 29 '17 at 20:21

score 3 · Answer 2 · edited May 29 '17 at 20:07

3

One return value is for wimps! Simply define the function as

struct retval { int i; double d; size_t z; } func(void);

(replacing the contents of the struct and the parameters as applicable).

Be careful when doing this, though. In spite of what I said up top, in general there is no need for multiple returns.

edited May 29 '17 at 20:07

David Ranieri

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answered May 29 '17 at 20:04

Gold Dragon

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score 1 · Answer 3 · answered May 29 '17 at 20:16

You can create a struct with all the things you are interested in, alloc it on heap, edit it inside a function, return the same struct that you have edited and at the end free the memory. Alternatively, you can also pass the pointer and at the end free the memory.

Example:

typedef struct date_test {
int year;
int month;
int day;
} Date;

With this you create a structure that will contain 3 int values: year, month and day.

Alloc it on heap and check for errors:

Date *test = malloc(sizeof(Date));
if (test == NULL) {
    perror("Malloc");
    exit(EXIT_FAILURE);
}

Edit it inside a function and return the struct, example:

Date* test_f(Date* test)
{
    test->year = 2017;
    test->month = 05;
    test->day = 29;
    return test;
}

Then free the allocated memory:

free(test);

You don't need to `return test;` in this case. – David Ranieri May 29 '17 at 20:20 — David Ranieri, May 29 '17 at 20:20

C programming, doing multiple calculations in one function

3 Answers3