Pointers in C — Revision Notes

Definition

Syntax

type *pointerName;
pointerName = &variable;
*pointerName;   // dereference: get the value

Example

#include <stdio.h>

int main() {
    int age = 25;
    int *ptr = &age;

    printf("Value: %d\n", age);
    printf("Address: %p\n", (void*)&age);
    printf("Via pointer: %d\n", *ptr);
    return 0;
}

Output

Important Points

• & means "address of"; * (on a declaration) means "pointer to", and (on a pointer variable) means "dereference".
• A pointer's type must match the type of variable it points to.
• Pointers make it possible to modify a caller's variable from inside a function (pass by reference).
• An uninitialized pointer holds a garbage address — dereferencing it is dangerous.

Common Mistakes

• Dereferencing an uninitialized or NULL pointer, which crashes the program.
• Confusing * in a declaration ("pointer to") with * in an expression ("dereference").
• Forgetting that array names already act like pointers — writing &arr when arr alone is often what you want.

Interview Tip