C Program 16: To Print The Fibonacci Series Using Recursion

Aim: To print fibonacci series
Fibonacci series is the one in which every third number is the sum of first two.
The series is 1,1,3,4,7,11,18....
//To print the fibonacci series using recursion
#include<stdio.h>
#include<conio.h>
int fibo(int x);
void main()
{
     int a=1, b=1, n,p;
     printf("Enter the number of digits you want to print: ");
     scanf("%d", &n);
     printf("The fibonacci series is:\n%d\n%d", 1 , 1);
     fibo(n);
     getch();
}
int fibo(int x)
{
    static int a =1 , b=1, temp, c;
    if (x-2==0)
    {
               return 0;
    }
    else
    {
        c=a+b;
        printf("\n%d", c);
        temp=b;
        b=c;
        a=temp;
        fibo(x-1); //using recursion
    }
}

The code is fairly simple. We have printed the first two number using a simple printf statement in the main function. Then we have called the fibo()
Now, say we want to print the first 25 numbers in the series. that would mean value of n is 25. But we have already printed first two numbers in main function. So, in the fibo(), in if statement, we would put a condition for x-2 numbers i.e. 23 numbers.
Now, we would use simple arithmetic operation c=a+b; 
This would give us the third number. Then we have performed swapping of the numbers. And then we have called the same fibo() function. 

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C Program 15: To Find the Factorial of a number using for loop

Aim: To find factorial of a number
Factorial of a number like 4 would be 4*3*2*1=24
Following would be the code:
// To find the factorial of a given number using for loop
#include<stdio.h>
#include<conio.h>
void main()
{
     int fact, a;
     printf("Enter the number: ");
     scanf("%d", &a);
     fact=factorial (a);
     printf("The factorial of the given number is: %d\n", fact);
     getch();
     
}
int factorial(int x)
{
    int f=1,i;
    for(i=x; i>=1; i--)
    {
             f=f*i;
    } 
    return f;
}

Just a for loop for(i=x; i>=1; i--) is used. 

In case, you want to do the same through recursion.. check this link:

TO FIND FACTORIAL OF A NUMBER USING RECURSION

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C Program 14: To Find The Factorial of a Number Using Recursion

Aim: To find the factorial using recursion.
What is Recursion? when a function calls itself, the phenomenon is referred to as recursion and it is one of the most powerful features of C. Most of the algorithms that are developed using C use recursion.
Code: 
// To find the factorial of a given number using recursion
#include<stdio.h>
#include<conio.h>
void main()
{
     int fact, a;
     printf("Enter the number: ");
     scanf("%d", &a);
     fact=factorial (a);
     printf("The factorial of the given number is: %d\n", fact);
     getch();
     
}
int factorial(int x)
{
    int f;
    if (x==1)
    {
            return(1);
    }
    else 
    {
         f=x*factorial(x-1); //using recursion
    }
    return f;
}

The real part is in the function factorial. The function takes x as a parameter which is the number whose factorial we want to find. Say, we want to find 4! that means x would be equal to 4.
Now, we would use if else statement. If the value of x is 1, the function would return 1. 
Else, the following formula would be used:
f=x*factorial(x-1);
Note that we are using the same function once again. We are using factorial() inside factorial().  This is RECURSION.
But this time the value passed to the function isn't 4. It is 3 i.e. 4-1
thus, on successive calls the function would call itself and pass parameters like - 4,3,2,1. When function has 1 as parameter, if statement would be executed and control would return to the second last function i.e. the one with parameter 2.
Thus, we would get 4*3*2*1 = 24

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C Program 13: To Swap Two Numbers Using Pointers

Aim: Swap two numbers using pointers.
Following is the code:
//To swap two numbers using pointers
#include<stdio.h>
#include<conio.h>
void swap(int *a, int *b)
{
     int temp;
     temp = *a;
     *a=*b;
     *b=temp;
    // printf ("The value of a is: %d \n ", *a );
     //printf("The value of b is: %d\n ", * b);
}
void main()
{
     int *a, *b;
     printf("enter the two numbers: ");
     scanf("%d%d", &a, &b);
     swap (&a,&b);
     printf ("The value of a is: %d \n", a );
     printf("The value of b is: %d \n ", b);
     getch();
}

Theory: We will perform the swapping in function swap. So, the function swap has two arguments - *a and *b. An * before a means a is actually the value at address of a. So, if the value at address of a is 53, *a would take up that value.
Now, we use the basic swapping operation. We will put the *a into a temporary variable and then *b into *a and again temp into *b. This concludes the swapping. Now, if we want to print the resulting numbers in the swap function itself, we will need to use *a and *b in printf statement instead of a and b. This is because we want to print the value at a and b. If we don't do that, address of the a and b would be printed or some garbage value.
Now, coming back to main function, we must make sure that we pass address of a and b (&a, &b) to the swap function else we won't receive the correct output.

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C Program 12: To Print The Given Rectangle Pattern

Aim: To print this pattern 

*-***********

***-*********

*****-*******

*******-*****

*********-***

***********-*

Code: 

#include<stdio.h>

#include<conio.h>

void main()

{

     int i, j, k;

     for (i=0; i<=5; i++)

     {

         for (j=1; j<=i+(i+1); j++)

         {

             printf("*");

         }

        printf("-");

        for (k=1; k<=11-(i+i); k++)

         {

             printf("*");

         }

         printf("\n"); 

     } 

getch();         

         

}

For this pattern we will need to use three for loops. First loop would be for the number of lines in our pattern. Those are 6 and that's why the condition in the first for loop is i<=5

Now, we will try to divide our pattern in our two parts - one on the left side of dash and other on the right side.

The one at left side is printed in series like 1,3,5,7,9,11. So, all we need to do is to try to use a condition on the second for loop which tries to print this series. This is done through the condition j<=i+(i+1) 

The condition may obviously vary depending upon an individual's logical ability.

Similarly, in the third for loop, we would try to reverse the series - 11,9,7,5,3,1 And hence we will get the desired pattern.

Output: 

In case, you still have doubts.. feel free to contact me. 

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C Program 11: To Print a Right Angled Triangle

Aim:  To print this pattern
*
**
***
****
*****
Code:
#include<stdio.h>
#include<conio.h>
void main()
{
     int i, j, n;
     printf("Click on number of lines you want to print: ");
     scanf("%d", &n);
     for (i=1; i<=n; i++)
      {
               for (j=1; j<=i; j++)
               {
                   printf("*");
               }
               printf("\n");
      }
getch();
}

Theory:  The pattern is the simplest pattern. One thing you should remember while creating patterns is that the first for loop is always for the number of lines you want to cover with your pattern. Here we have asked the user to enter how many lines he wants to print the pattern in.
Then we have used the condition for (i=1; i<=n; i++) to print the stars according to the way we want. The choice is condition depends upon your logical capabilities and may differ.
This is the output:

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C Program 10: To Find The Smallest Number in an Array

Aim: To Find the smallest number in an array
Code:
#include<stdio.h>
#include<conio.h>
void main()
{
     int i, arr[5], smallest;
     printf("Enter the values in an array: ");
     for (i=0; i<=5; i++) /* enter values into array */
     {
         scanf("%d", &arr[i]);
     }
     /* checking the smallest no. */
     smallest = arr[0];
     for (i=0; i<=5; i++)
     {
         if (arr[i] < smallest )
         {
                    smallest = arr[i];
         }
     }
     printf("The smallest number is: %d", smallest);
     getch();
     
}

First we will ask the user to enter the values into the array. Now, we will take an integer smallest and put the initial value of array arr[0] into it.  Now, we have to compare each value present in array with the smallest. If this value is less than the value in  smallest we will replace the value of the latter with the value present in array at that time.

We will repeat that procedure 6 times for our array contains six values.

Following is the sample output:

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