Advanced · C PROGRAMMING

Pointers and addresses

What you will learn

Use an address to access an existing object.

Understand the concept

The & operator obtains an object address. A pointer stores an address of a compatible type. Applying * to a valid pointer accesses the pointed-to object. Changing *p here changes value, because p points to value.

Read the example

The complete program appears below. Read it first, predict the output, then run it.

Expected output

Value: 25

Practise

Create a second integer and redirect p to it before assigning through *p.

Common mistake

Do not dereference an uninitialized, null or expired pointer. The pointed-to object must still exist.

Lesson discussion

#include <stdio.h>

int main(void) {
    int value = 10;
    int *p = &value;
    *p = 25;
    printf("Value: %d\n", value);
    return 0;
}

PRACTICE LAB

Read. Edit. Run.

C source · .c

Experiment with the program below. Your code and input are sent to the selected compiler only when you run it.

Compiler

C source

Tab indents · Shift+Tab unindents · Esc then Tab leaves the editor · Ctrl/Cmd+Enter runs · Ctrl/Cmd+S saves a draft

Changes save automatically to your account.

Standard input

Input / output example

Example input

No input required.

Expected output for the original program

Value: 25

Output will appear here.

Pointers and addresses

What you will learn

Understand the concept

Read the example

Expected output

Practise

Common mistake

Lesson discussion

Read. Edit. Run.

Input / output example

Debugging Lab

Interactive Memory Visualizer

Stack frames

Memory and pointers

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