In C, Arrays are always passed as reference while scalar Variables and Structures are passed as value

array_builtin_fun_arg.c

#include <stdio.h>
#include <string.h>

void printArray(int a[]) {
    int i = 0;
    for(i = 0; i < 10; i++) {
        printf("%d ", a[i]);
    }
    printf("\n");
}

void changesArray(int a[10]) {
    int i = 0;
    for(i = 0; i < 10; i++) {
       a[i] += 5;
    }
}

main()
{
   int a[10] = {0};
   int i = 0;
   
   for(i = 0; i < 10; i++) {
       a[i] = i;
   }
   
   printArray(a);
   changesArray(a);
   printArray(a);
}

struct_fun_arg.c

#include <stdio.h>
#include <string.h>

typedef struct Struct {
  int a;  
} Struct;

void printStruct(Struct st) {
    printf("%d\n", st.a);
}

void changesStruct(Struct st) {
    st.a++;
    printStruct(st);
}

main()
{
   Struct st = {5};
   
   printStruct(st);
   changesStruct(st);
   printStruct(st);
}