Structs and passing values to them - c

Question

If i had an array such as int numbers[5] i could assign values to it with numbers[0] = 1 or numbers[3] = 4. Then if i had a struct such as
struct structName
{
int number0;
int number1;
int number2;
};
is there any way to do something like the following (note this is not working code)
int main(void)
{
struct structName name; //how could i declare this to do the following
for(int i = 0; i < 2; i++)
{
name[i] = i; //maybe name.[i]
}
}
so is there a way to write name[ variable ] = someNumber to assign someNumber to say number0 (if variable was 0) or number2 (if variable was 2). ive been looking for days and cant find anything that does this. (maybe i just don't know what to look for)

Answer 1

is there any way to do something like the following
No, there's no way to access the fields of the structure by index. You use the names of the fields instead:
struct structName name;
name.number0 = someNumber;
name.number1 = someOtherNumber;
If you want to access the values by index, use an array instead, even if it's embedded in the structure:
struct structName
{
int numbers[3];
// other fields here
};
Then you can say:
struct structName name;
for (int i = 0; i <= 2, i++) {
name.numbers[i] = i;
}

Answer 2

You could write a function which uses a switch statement that allows you to access fields by index. Something like:
#include<stdio.h>
struct structName{
int number0;
int number1;
int number2;
};
void assign(struct structName * name, int i, int j){
switch(i){
case 0:
name->number0 = j;
break;
case 1:
name->number1 = j;
break;
case 2:
name->number2 = j;
break;
}
}
int main(void){
int i;
struct structName name;
for(i = 0; i <= 2; i++){
assign(&name,i,i);
}
//test:
printf("%d\n",name.number0);
printf("%d\n",name.number1);
printf("%d\n",name.number2);
return 0;
}
(which prints 0,1,2 as expected).
Needless to say, there isn't much point in doing this (as opposed to just having a field which is an array) unless the struct in question is already defined as part of an API or already part of a code base which isn't easily refactored.

Answer 3

Yes, with some weird and inadvisable memory manipulation. You're much better off using an array.
struct structName
{
int numbers[3];
};
int main(void)
{
struct structName name;
for(int i = 0; i <= 2; i++)
{
name.numbers[i] = i;
}
}
Also note that you had some syntax errors in your for loop and an off-by-one error.

Answer 4

Macros with arguments should work
#define name(x) x
So name(1) would become 1. name(2) would become 2 and so on.

Answer 5

In C, there is no spoon.
struct structName name;
int *idx = &name; // First we need a memory address to the struct
for (int i = 0; i < sizeof(name) / sizeof(*idx); ++i) {
// idx[i] == name.numberX
idx[i] = i;
}
Now, if you check the values of name.number0, name.number1, name.number2 you will see they contain the correct values.
This is not a very good way of doing things with structs, but I felt compelled to answer after the top response claims it is impossible.