Notice: This page requires JavaScript to function properly.
Please enable JavaScript in your browser settings or update your browser.Learn Functions, Arrays and Two Pointers | Pointers
C Basics
course content

Course Content

C Basics

C Basics

1. Introduction
Structure of the C-ProgramEssentials of C ProgramHow to Run the Program?
2. Data
DataVariablesPrintfIntroduction to ArraysTwo Dimensional ArraysChar and StringSizeofPrintf PracticeSizeof Practice
3. Operators
Assignment, Comparison, Not Equal ToSum, Difference, Increment, DecrementMultiplication, Division and ModuloComparison OperatorsComparison Operators PracticeLogical OperatorsLogical Operators Practice
4. Control Statements
If-else Operatorif-else Operator PracticeTernary OperatorSwitch, BreakWhile, Do-WhileFor, ContinueFor Loop Practice
5. Functions
Structure of the FunctionDeclaration, Type and ReturnArgumentsPassing ArgumentsHeader, Prototypes Void, Recursion
6. Pointers
Pointers are around UsReferences and DereferencesPointersMalloc and FreeFunctions, Arrays and Two PointersVoid

book
Functions, Arrays and Two Pointers

Functions with Pointers

Let's experiment with a basic function to modify the value of our data. For instance, imagine you need a function that converts kilo-Ohms to Ohms (1 kOhm = 1000 Ohm).

c

Main

copy

              
12345678910111213141516171819

            
#include <stdio.h>

void Ohm(double R)
{
    R = R * 1000;
}

int main()
{
    double r = 1.5; // kOhm
  
    printf("The value of resistance before using function: %f\n", r);

    Ohm(r);

    printf("The value of resistance after using function: %f", r);

    return 0;
}

Our attempt to change the value of the r variable was unsuccessful. This is because the function receives a copy of the r variable, not the actual value itself.

To make our program work as intended, we need to pass the address of the r variable to the function. As a result, the Ohm function should accept double* instead of just double.

c

Main

copy

              
1234567891011121314151617181920

            
#include <stdio.h>

void Ohm(double* R)
{
    // dereferencing the entered address and changing the object it points to
    *R = *R * 1000;
}

int main()
{
    double r = 1.5; // kOhm

    printf("The value of resistance before using function: %f\n", r);

    Ohm(&r);

    printf("The value of resistance after using function: %f\n", r);

    return 0;
}

Note that we reference the r variable twice. After invoking the Ohm function, the value of r is altered. This is because the function received the original address of the variable r, not a mere copy, and then modified the value at that particular address.

Moreover, a function can return a pointer to an object that it has generated:

c

Main

copy

              
1234567891011121314151617181920

            
#include <stdio.h>
#include <stdlib.h>

int* func()
{
    int* x = (int*)malloc(sizeof(int));

    printf("Address into function: %p\n", x);

    return x;
}

int main()
{
    int* pointerToFunc = func();

    printf("Address after using function: %p\n", pointerToFunc);
   
    return 0;
}

Are Arrays Merely Pointers?

What do you predict will transpire if a number is appended to an address?

c

Main

copy

              
123456789101112

            
#include <stdio.h>

int main()
{
    int x = 100;

    int* pX = &x;

    printf("Address: %p | Adress + 1: %p", pX, pX + 1);

    return 0;
}

When a number (pX + 1) is added to an address, it yields the address of the subsequent memory cell!

Let's script a loop to navigate the "sequence" of RAM:

c

Main

copy

              
1234567891011

            
#include <stdio.h>

int main()
{
    int* pX = NULL; // pointer to `int` type (4 bites)

    for (int i = 0; i < 3; i++)
        printf("Address: %p\n", pX + i);

    return 0;
}

We've projected three steps ahead. It's apparent from the derived addresses that there's a clear hierarchy.

Given that the int type occupies 4 bytes, we progress by 4 bytes with each step. This behavior is strikingly reminiscent of an array!

It seems an array is essentially a fixed address (represented by the array's name) coupled with allocated memory. The indices of the elements represent their offset from the address of the initial element!

This notion can be validated with the following program:

c

Main

copy

              
12345678910111213

            
#include <stdio.h>

int main()
{
    int array[] = {1,2,3,4,5};

    printf("Address of array: %p\n", array);

    for(int i = 0; i < 5; i++)
        printf("Value: %d | Address of element with index %d: %p\n", *(array + i), i , &array[i]);

    return 0;
}

As observed, we don't traverse directly through the array. We solely utilize its address, specifically the address of its initial element.

Everything was clear?

How can we improve it?

Thanks for your feedback!

SectionΒ 6. ChapterΒ 5

Ask AI

expand
ChatGPT

Ask anything or try one of the suggested questions to begin our chat

course content

Course Content

C Basics

C Basics

1. Introduction
Structure of the C-ProgramEssentials of C ProgramHow to Run the Program?
2. Data
DataVariablesPrintfIntroduction to ArraysTwo Dimensional ArraysChar and StringSizeofPrintf PracticeSizeof Practice
3. Operators
Assignment, Comparison, Not Equal ToSum, Difference, Increment, DecrementMultiplication, Division and ModuloComparison OperatorsComparison Operators PracticeLogical OperatorsLogical Operators Practice
4. Control Statements
If-else Operatorif-else Operator PracticeTernary OperatorSwitch, BreakWhile, Do-WhileFor, ContinueFor Loop Practice
5. Functions
Structure of the FunctionDeclaration, Type and ReturnArgumentsPassing ArgumentsHeader, Prototypes Void, Recursion
6. Pointers
Pointers are around UsReferences and DereferencesPointersMalloc and FreeFunctions, Arrays and Two PointersVoid

book
Functions, Arrays and Two Pointers

Functions with Pointers

Let's experiment with a basic function to modify the value of our data. For instance, imagine you need a function that converts kilo-Ohms to Ohms (1 kOhm = 1000 Ohm).

c

Main

copy

              
12345678910111213141516171819

            
#include <stdio.h>

void Ohm(double R)
{
    R = R * 1000;
}

int main()
{
    double r = 1.5; // kOhm
  
    printf("The value of resistance before using function: %f\n", r);

    Ohm(r);

    printf("The value of resistance after using function: %f", r);

    return 0;
}

Our attempt to change the value of the r variable was unsuccessful. This is because the function receives a copy of the r variable, not the actual value itself.

To make our program work as intended, we need to pass the address of the r variable to the function. As a result, the Ohm function should accept double* instead of just double.

c

Main

copy

              
1234567891011121314151617181920

            
#include <stdio.h>

void Ohm(double* R)
{
    // dereferencing the entered address and changing the object it points to
    *R = *R * 1000;
}

int main()
{
    double r = 1.5; // kOhm

    printf("The value of resistance before using function: %f\n", r);

    Ohm(&r);

    printf("The value of resistance after using function: %f\n", r);

    return 0;
}

Note that we reference the r variable twice. After invoking the Ohm function, the value of r is altered. This is because the function received the original address of the variable r, not a mere copy, and then modified the value at that particular address.

Moreover, a function can return a pointer to an object that it has generated:

c

Main

copy

              
1234567891011121314151617181920

            
#include <stdio.h>
#include <stdlib.h>

int* func()
{
    int* x = (int*)malloc(sizeof(int));

    printf("Address into function: %p\n", x);

    return x;
}

int main()
{
    int* pointerToFunc = func();

    printf("Address after using function: %p\n", pointerToFunc);
   
    return 0;
}

Are Arrays Merely Pointers?

What do you predict will transpire if a number is appended to an address?

c

Main

copy

              
123456789101112

            
#include <stdio.h>

int main()
{
    int x = 100;

    int* pX = &x;

    printf("Address: %p | Adress + 1: %p", pX, pX + 1);

    return 0;
}

When a number (pX + 1) is added to an address, it yields the address of the subsequent memory cell!

Let's script a loop to navigate the "sequence" of RAM:

c

Main

copy

              
1234567891011

            
#include <stdio.h>

int main()
{
    int* pX = NULL; // pointer to `int` type (4 bites)

    for (int i = 0; i < 3; i++)
        printf("Address: %p\n", pX + i);

    return 0;
}

We've projected three steps ahead. It's apparent from the derived addresses that there's a clear hierarchy.

Given that the int type occupies 4 bytes, we progress by 4 bytes with each step. This behavior is strikingly reminiscent of an array!

It seems an array is essentially a fixed address (represented by the array's name) coupled with allocated memory. The indices of the elements represent their offset from the address of the initial element!

This notion can be validated with the following program:

c

Main

copy

              
12345678910111213

            
#include <stdio.h>

int main()
{
    int array[] = {1,2,3,4,5};

    printf("Address of array: %p\n", array);

    for(int i = 0; i < 5; i++)
        printf("Value: %d | Address of element with index %d: %p\n", *(array + i), i , &array[i]);

    return 0;
}

As observed, we don't traverse directly through the array. We solely utilize its address, specifically the address of its initial element.

Everything was clear?

How can we improve it?

Thanks for your feedback!

SectionΒ 6. ChapterΒ 5
We're sorry to hear that something went wrong. What happened?
some-alt