Value parameter

void display(struct Student s) receives a structure value. Changes to s.roll or s.marks inside that function affect only the parameter object. This provides a simple interface when a record should not be replaced by the function.

Pointer parameter

void update(struct Student *p) can assign p->marks. The arrow operator accesses a member of the structure identified by p; p->marks means (*p).marks. The caller passes &student. A reading function can take const struct Student *p to prevent member modification through that access.

Example trace

The complete example starts with marks 70. update(&s, 80) receives the address and assigns p->marks = 80. main then displays 80, because the original object was modified. Passing a pointer is still C pass by value: the copied value is an address.

Validity and output

A pointer must identify a live, suitable structure object. Checking against NULL does not prove every non-null address is valid. Output can be a returned scalar, a returned structure or an object changed through a pointer, depending on the interface.

Complexity

For this fixed-size record, the update takes O(1) work and space. For larger records, value passing can involve copying the record representation; using a pointer avoids explicitly requesting a full record copy at the source interface. Pointer members still need separate ownership rules.

Complete C example

main.c

/* CodeBhavya | Data Structures AR25 | Learning example */
#include <stdio.h>
struct Student { int roll, marks; };
void update(struct Student *p, int marks)
{
    if (p != NULL) { p->marks = marks; }
}

int main(void)
{
    struct Student s = {101, 70};
    update(&s, 80);
    printf("Marks = %d\n", s.marks);
    return 0;
}

Marks = 80