Introduction to Pointers

Understand pointers with the help of a simple example.

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Pointers

Pointers are like any other variables. Their specialty, however, is storing addresses of other variables.

Pointers are variables that hold the addresses of other variables.

Pointer declaration

The basic syntax for declaring a pointer is given below:

dataType * variableName;

Example program

Let’s understand pointers with the help of a simple example. Press the RUN button and see the output!

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# include <stdio.h>

int main( )

{

	// Initializes variable i

	int  i = 3 ;

	// Declares pointer j

	int  *j ;

	// Stores the address of i in j

	j = &i ;

	

	// Prints address of i 

	printf ( "Address of i = %u\n", &i ) ;

	printf ( "Address of i = %u\n", j ) ;

	// Prints address of j

	printf ( "Address of j = %u\n", &j ) ;





    // Prints value of i

	printf ( "Value of i = %d\n", i ) ;

	printf ( "Value of i = %d\n", *( &i ) ) ;

	printf ( "Value of i = %d\n", **&j) ;

	printf ( "Value of i = %d\n", *j ) ;

	// Prints value of j

	printf ( "Value of j = %u\n", j ) ;

	printf ( "Value of j = %u\n", *&j) ;

	

	return 0 ;

}

Explanation

Lines 7-9: the difference between an integer and an address

An address permits limited arithmetic, i.e., pointer + number, pointer - number, and pointer - pointer. All other arithmetic is not permitted. This will be further explained later in the course.

  • int *j means the value at the address stored in j is an integer. This declaration informs the compiler that j will store an address of an integer, not an integer itself, so j is defined to be of the type int *.

  • j = &i means we are storing the address of variable i in j, i.e., 4096; j itself might be given the location, 4160, or any such location.

Lines 12-13: We can get the address of i through the expressions: j or &i.

Line 15: We can get the address of j through the expression: &j.

Lines 19-22: The value of i can be printed using the expressions: i, *&i, *j, and **&j.

Lines 24-25: To get the value of j, we can either use j or *&j.

📝 Note: Since j is the same as *&j, in the expression: *j; j can be replaced with *&j, resulting in the expression: **&j. Moreover, *&j is same as *(&j).

Pointers store whole numbers

See the output of the code given below!

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#include<stdio.h>



int main() {

    // Initializes variable ch and f

    char ch = 'a';

    float f = 1.5;

    // l stores an address of char variable

    char *l;

    l = &ch;

    // m stores an address of float variable

    float *m;

    m = &f;

    // Prints address of l and m

    printf ( "Value of l = %u\n", l ) ;

    printf ( "Value of m = %u\n", m ) ;



    return 0;

}

In the code above, l and m are pointer variables, and they will store whole numbers. Keep in mind that addresses are whole numbers; therefore, pointers always store whole numbers.

Line 8: char *l informs the compiler that l will store an address of a char value, not the char value itself.

Line 11: Similarly, float *m informs the compiler that m will store an address of a floating-point value, not the floating-point value itself.