C programming - Part 19

C Program To Swap Two Numbers using Pointers

Lets write a C program to swap 2 numbers using pointers and function.

When we call the function, we pass the reference or address of the variable, so this method is called “Call by Reference“.

Video Tutorial: C Program To Swap Two Numbers using Pointers

[youtube https://www.youtube.com/watch?v=snxBqbRYrhs]

YouTube Link: https://www.youtube.com/watch?v=snxBqbRYrhs [Watch the Video In Full Screen.]

Source Code: C Program To Swap Two Numbers using Pointers and Function

#include<stdio.h>

void swap(int*, int*);

int main()
{
    int a, b;

    printf("Enter values for a and b\n");
    scanf("%d%d", &a, &b);

    printf("\n\nBefore swapping: a = %d and b = %d\n", a, b);

    swap(&a, &b);

    printf("\nAfter swapping: a = %d and b = %d\n", a, b);

    return 0;
}

void swap(int *x, int *y)
{
    int temp;

    temp = *x;
    *x   = *y;
    *y   = temp;
}

Output 1:
Enter values for a and b
100
200

Before swapping: a = 100 and b = 200

After swapping: a = 200 and b = 100

Output 2:
Enter values for a and b
30
20

Before swapping: a = 30 and b = 20

After swapping: a = 20 and b = 30

Logic To Swap Two Numbers using Pointers and Function

We ask the user to enter values for variable a and b. We pass the address of variable a and b to function swap().

Inside function swap() we take a local variable temp. Since address of variable a and b are passed to swap() method, we take 2 pointer variables *x and *y. Pointer variable x holds the address of a and pointer variable y holds the address of b. Using below logic we swap the values present at address a( or x ) and b( or y ).

temp = *x;
*x = *y;
*y = temp;

Since we are directly changing the value present at particular address, the value gets reflected throughout the program and not just inside particular function. That’s why we are able to print the result inside main function and the values of variable a and b are swapped, without getting any returned value from function swap().

For list of all c programming interviews / viva question and answers visit: C Programming Interview / Viva Q&A List

For full C programming language free video tutorial list visit:C Programming: Beginner To Advance To Expert

C Program To Add Two Numbers using Pointers

Lets write a C program to add 2 numbers using pointer and function.

In this video tutorial we will show both ways of adding 2 numbers using pointers: 1. Using function 2. Without using function.

Video Tutorial: C Program To Add Two Numbers using Pointers

[youtube https://www.youtube.com/watch?v=0wBPwxsr6-U]

YouTube Link: https://www.youtube.com/watch?v=0wBPwxsr6-U [Watch the Video In Full Screen.]

Source Code: C Program To Add Two Numbers using Pointers and Without using Function

#include<stdio.h>

int main()
{
    int a, b, c, *ptr1, *ptr2;

    ptr1 = &a;
    ptr2 = &b;

    printf("Enter 2 numbers\n");
    scanf("%d%d", &a, &b);

    c = *ptr1 + *ptr2;

    printf("Using *ptr1 + *ptr2 : %d + %d = %d\n", a, b, c);

    c = *(&a) + *(&b);

    printf("Using  *(&a) + *(&b) : %d + %d = %d\n", a, b, c);

    return 0;
}

Output:
Enter 2 numbers
25
25
Using *ptr1 + *ptr2 : 25 + 25 = 50
Using (&a) + *(&b) : 25 + 25 = 50

Logic To Add Two Numbers using Pointers

Here we are storing the address of variable a in pointer variable ptr1 and address of variable b in pointer variable ptr2.

We know that any address preceded by * would fetch the value present at that address. So we use following code to get the addition of 2 numbers result using pointers.

c = *ptr1 + *ptr2;

Source Code: C Program To Add Two Numbers using Pointer and Function

#include<stdio.h>

void addition(int, int, int*);

int main()
{
    int a, b, c;

    printf("Enter 2 numbers\n");
    scanf("%d%d", &a, &b);

    addition(a, b, &c);

    printf("%d + %d = %d\n", a, b, c);

    return 0;
}

void addition(int x, int y, int *z)
{
    *z = x + y;
}

Output:
Enter 2 numbers
10
40
10 + 40 = 50

Logic To Add Two Numbers using Pointers and Function

We ask the user to enter 2 numbers and store it inside address of variables a and b. Next we pass the values of a and b and address of variable c to a function called addition(). And then print the result in main method itself.

The motive is to change the value present at address of variable c. That way we can print the result directly inside main method itself, without our function addition() returning any value back to calling function(main()).

Inside addition() method, we add the values passed in first 2 arguments and then store the result back in the address location sent to addition() function as third argument. Function addition() doesn’t return any value, so it has void as its return type.

For list of all c programming interviews / viva question and answers visit: C Programming Interview / Viva Q&A List

For full C programming language free video tutorial list visit:C Programming: Beginner To Advance To Expert

Basics of Pointers In C Programming Language

In today’s video tutorial lets learn basics of pointers in C programming language. Think of it as base of a building. If you can hold these basic concepts strong your building will be safer.

Topics Covered

1. What are pointers?
2. How to declare pointers.
3. How to access the value present at the address stored in pointer variable.
4. Using Address of operator.
5. Using Indirection operator.

What are pointers?

A pointer is a variable which refers to or points to an address in your computers memory.

Definition: A pointer variable is a variable which holds the address of another variable.

And since pointer variable is also a variable, it also has a unique address associated with it.

Operators

& is called “address of” operator.
* is called Indirection or “value at address” operator.

Video Tutorial: Basics of Pointers In C Programming Language

[youtube https://www.youtube.com/watch?v=1R6dBm3LN68]

YouTube Link: https://www.youtube.com/watch?v=1R6dBm3LN68 [Watch the Video In Full Screen.]

Source Code: Basics of Pointers In C Programming Language

#include<stdio.h>

int main()
{
    int num = 5;
    int *ptr; // pointer variable

    ptr = &num; // both hold address of num

    printf("Value of num = %d\n", num);
    printf("Address of num = %d\n", &num);
    printf("Address of ptr = %d\n", &ptr);
    printf("Value of ptr = %d\n", ptr);
    printf("Access value of num from ptr = %d\n", *ptr);
    printf("Access value of num from num = %d\n", *(&num));

    return 0;
}

Output:
Value of num = 5
Address of num = 6356732
Address of ptr = 6356728
Value of ptr = 6356732
Access value of num from ptr = 5
Access value of num from num = 5

Note: Whenever you declare and initialize a variable, for example, int num = 5; Your program does the following tasks:
1. Reserves space in your computers memory depending upon the data type.
2. Associates the name num with this memory location.
3. Stores the number 5 in this memory location.

Declaration of pointer variable

General Syntax
data_type* pointer_variable_name;

data_type *pointer_variable_name;

Example:

int *ptr1;

int* ptr2;

Both these declaration are valid.

Rules for constructing pointer variable are same as that of regular variables: Rules for Constructing Variable Names: C

Assigning value to pointer variable

General Syntax
pointer_variable_name = &another_variable;

Example:

ptr = &num;

This stores the address of variable num as value of pointer variable ptr.

Declaring and Assigning value to pointer variable

Example:

int num = 5;
int *ptr;  // Declaration of pointer variable

ptr = &num;  // Assigning value to pointer variable

Note: While assigning address to pointer variable do not include * in front of pointer variable.

Values and addresses

num will have 5.
&num will have address of num.
&ptr will have address of ptr.
ptr will have address of num.
*ptr will have value of num.

Call by Value and Call by reference

Call by Value Example: C Program To Swap Two Numbers using Function
Call by Reference Example: C Program To Swap Two Numbers using Pointers

Note: Address can’t be negative values. So we can use %u as format specifier, which means unsigned integer.

For list of all c programming interviews / viva question and answers visit: C Programming Interview / Viva Q&A List

For full C programming language free video tutorial list visit:C Programming: Beginner To Advance To Expert

C Program To Print Multiplication Table Using Function

Lets write a C program to print the multiplication table for a user input number, using function/method. The table should get displayed in the following format:

Example: Multiplication table of 5
5 x 1 = 5
5 x 2 = 10
5 x 3 = 15
5 x 4 = 20
5 x 5 = 25
5 x 6 = 30
5 x 7 = 35
5 x 8 = 40
5 x 9 = 45
5 x 10 = 50

Coding Challenge on Numbers!
Print the multiplication table which gives the following output:

multiplication table for number 37

Hint: Initialize count to 3. Increment the value of count by 3 for each iteration of for loop.

Answer: We’ve posted the source code to above coding challenge at the end of this blog post.

Video Tutorial: C Program To Print Multiplication Table Using Function

[youtube https://www.youtube.com/watch?v=5fafT5Pc1jw]

YouTube Link: https://www.youtube.com/watch?v=5fafT5Pc1jw [Watch the Video In Full Screen.]

Source Code: C Program To Print Multiplication Table Using Function

#include<stdio.h>

void tables(int);

int main()
{
    int num;

    printf("Enter a positive number\n");
    scanf("%d", &num);

    printf("\nMultiplication Table for %d is:\n", num);

    tables(num);

    return 0;
}

void tables(int num)
{
    int count;

    for(count = 1; count <= 10; count++)
    {
        printf("%d x %d = %d\n", num, count, num*count);
    }
}

Output 1:
Enter a positive number
5

Multiplication Table for 5 is:
5 x 1 = 5
5 x 2 = 10
5 x 3 = 15
5 x 4 = 20
5 x 5 = 25
5 x 6 = 30
5 x 7 = 35
5 x 8 = 40
5 x 9 = 45
5 x 10 = 50

Output 2:
Enter a positive number
2

Multiplication Table for 2 is:
2 x 1 = 2
2 x 2 = 4
2 x 3 = 6
2 x 4 = 8
2 x 5 = 10
2 x 6 = 12
2 x 7 = 14
2 x 8 = 16
2 x 9 = 18
2 x 10 = 20

Output 3:
Enter a positive number
7

Multiplication Table for 7 is:
7 x 1 = 7
7 x 2 = 14
7 x 3 = 21
7 x 4 = 28
7 x 5 = 35
7 x 6 = 42
7 x 7 = 49
7 x 8 = 56
7 x 9 = 63
7 x 10 = 70

Output 4:
Enter a positive number
9

Multiplication Table for 9 is:
9 x 1 = 9
9 x 2 = 18
9 x 3 = 27
9 x 4 = 36
9 x 5 = 45
9 x 6 = 54
9 x 7 = 63
9 x 8 = 72
9 x 9 = 81
9 x 10 = 90

Logic: Multiplication Table

User enters a positive number, we store it inside variable num. We pass this number entered by the user to a function called tables().

Inside tables() function we write a for loop. We initialize the for loop counter variable count to 1 and iterate through this for loop until count is less than or equal to 10 – because we want to display multiplication tables from 1 to 10. For each iteration of for loop we increment the value of count by 1.

Inside for loop we display the multiplication table.

You can also watch C Program To Print Multiplication Table Using While Loop video tutorial.

Just For Some Number Fun

Here I’m initializing 3 to count variable. For loop executes until count is less than or equal to 27. For each iteration of for loop count value increments by 3.

We assign 37 to num variable. Check the output.

Source Code: Some numerology!

#include<stdio.h>

void tables(int);

int main()
{
    int num = 37;

    printf("\nMultiplication Table for %d is:\n", num);

    tables(num);

    return 0;
}

void tables(int num)
{
    int count;

    for(count = 3; count <= 27; count += 3)
    {
        printf("%d x %d = %d\n", num, count, num*count);
    }
}

Output:
Multiplication Table for 37 is:

37 x 3 = 111
37 x 6 = 222
37 x 9 = 333
37 x 12 = 444
37 x 15 = 555
37 x 18 = 666
37 x 21 = 777
37 x 24 = 888
37 x 27 = 999

For list of all c programming interviews / viva question and answers visit: C Programming Interview / Viva Q&A List

For full C programming language free video tutorial list visit:C Programming: Beginner To Advance To Expert

C Program To Convert Year To Roman Equivalent

Write a general-purpose function to convert any given year into its Roman equivalent. Use these Roman equivalents for decimal numbers:

1 – i, 5 – v, 10 – x, 50 – l, 100 – c, 500 – d, 1000 – m.

Example:
Roman equivalent of 1988 is mdcccclxxxviii.
Roman equivalent of 1525 is mdxxv.

Chart for Roman equivalents of decimal numbers

Decimal	Roman Equivalent
1000	m
500	d
100	c
50	l
10	x
5	v
1	i

Video Tutorial: C Program To Convert Year To Roman Equivalent

[youtube https://www.youtube.com/watch?v=oocEj-8u4o8]

YouTube Link: https://www.youtube.com/watch?v=oocEj-8u4o8 [Watch the Video In Full Screen.]

Spurce Code: C Program To Convert Year To Roman Equivalent

#include<stdio.h>

void roman(int num)
{
    while(num)
    {
        if(num >= 1000)
        {
            printf("m");
            num = num - 1000;
        }
        else if(num >= 500)
        {
            printf("d");
            num = num - 500;
        }
        else if(num >= 100)
        {
            printf("c");
            num = num - 100;
        }
        else if(num >= 50)
        {
            printf("l");
            num = num - 50;
        }
        else if(num >= 10)
        {
            printf("x");
            num = num - 10;
        }
        else if(num >= 5)
        {
            printf("v");
            num = num - 5;
        }
        else if(num >= 1)
        {
            printf("i");
            num = num - 1;
        }
    }

    printf("\n");
}

int main()
{
    int year;

    printf("Input the year to get its Roman Equivalent\n");
    scanf("%d", &year);

    roman(year);

    return 0;
}

Output 1:
Input the year to get its Roman Equivalent
1988
mdcccclxxxviii

Output 2:
Input the year to get its Roman Equivalent
1525
mdxxv

Output 3:
Input the year to get its Roman Equivalent
2500
mmd

Output 4:
Input the year to get its Roman Equivalent
2020
mmxx

Output 5:
Input the year to get its Roman Equivalent
2021
mmxxi

Logic To Convert Year To Roman Equivalent

We ask the user to enter the year in decimal number format and store it inside variable year. Next we pass this user input year to function roman.

Inside function roman, we copy the value of year to a local variable num. We write a while loop and iterate until value of num is positive. Control exits while loop once num is equal to 0.

Inside while loop we check if the value of num is greater than or equal to 1000. If true, then we print roman equivalent of 1000, which is m. And then we decrement the value of num by 1000.

For each iteration of the while loop we check if num is greater than or equal to 1000 or 500 or 100 or 50 or 10 or 5 or 1. To whichever number the value of num matches we printout its corresponding representation in roman:

i.e., 1 – i, 5 – v, 10 – x, 50 – l, 100 – c, 500 – d, 1000 – m.

and also immediately decrement the value by its matched decimal equivalent. We keep doing this until num value is 0.

Example:

If user input year is 1525

Iteration	num	Match	Roman Equivalent	New Value of num
1	1525	1000	m	525
2	525	500	d	25
3	25	10	x	15
4	15	10	x	5
5	5	5	v	0

In above table, last value of num is 0, so control exits while loop. So roman equivalent of year 1525 is mdxxv.

For list of all c programming interviews / viva question and answers visit: C Programming Interview / Viva Q&A List

For full C programming language free video tutorial list visit:C Programming: Beginner To Advance To Expert