Write a program to check a given number is prime or not

1. Write a program to checka givennumberisprime ornot.
Algorithm:
Step1: Start
Step2: Declare variablesn,i,prime.
Step3: Initialize variables
prime←0
i←2
Step4: Readn fromuser.
Step5: Repeatthe stepsuntil i<=(n/2)
5.1 If remainderof n÷i equals0
prime←1
Go to step6
5.2 i←i+1
Step6: If prime=0
Displayn isprime
else
Displayn isnot prime
Step7: Stop
Source Code:
#include<stdio.h>
voidmain()
{inti,n,prime=0;
printf("Enteranynumber:");
scanf("%d",&n);
i=2;
while(i<=n/2)
{if(n%i==0)
{prime=1;
break;
}
i++;
}
if(prime==0)
printf("nItisa prime number");
else
printf("nItisnota prime number");
}

Output:
Discursion:
If the while loop terminates when the test expression of loop i <= n/2 is false, the entered
number is a prime number. The value of prime is equal to 0 in this case.
2. Write a c program to check whether a number is a krishnamurty number or not
Algorithm:
1. Input a number from user to check for strong number. Store this in a variable say num.
Copy it to a temporary variable for calculations purposes, say originalNum = num.
2. Initialize another variable to store sum of factorial of digits, say sum = 0.
3. Find last digit of the given number num. Store the result in a variable say lastDigit =
num % 10.
4. Find factorial of lastDigit. Store factorial in a variable say fact.
5. Add factorial to sum i.e. sum = sum + fact.
6. Remove last digit from num as it is not needed further.
7. Repeat steps 3 to 6 till num > 0.
8. After loop check condition for strong number. If sum == originalNum, then the given
number is Strong number otherwise not.
#include <stdio.h>
voidmain()
{
int i,originalNum,num,lastDigit,sum;
longfact;
printf("Enteranynumbertocheckkrishnamurtynumber:");
scanf("%d",&num);

originalNum=num;
sum = 0;
while(num>0)
{
lastDigit=num %10;
fact= 1;
for(i=1;i<=lastDigit;i++)
{
fact = fact * i;
}
sum= sum+ fact;
num= num/ 10;
}
if(sum== originalNum)
{
printf("%diskrishnamurtyNUMBER",originalNum);
}
else
{
printf("%disNOTkrishnamurtyNUMBER",originalNum);
}
}
3. Fibonacci seriesusingrecursive functioninC
#include<stdio.h>
intFibonacci(int);
intmain()
{
intn, i = 0, c;
printf("nEnterhowmanytermyouwantin Fibonacci series:");
scanf("%d",&n);

printf("nFibonacci series:");
for ( c = 1 ; c <= n ; c++ )
{
printf("%dt",Fibonacci(i));
i++;
}
}
intFibonacci(intn)
{
if ( n == 0 )
return0;
else if ( n == 1 )
return1;
else
return( Fibonacci(n-1) +Fibonacci(n-2) );
}
Discursion:
Fibonacci series is a sequence of following numbers
0 1 1 2 3 5 8 13 ....
It adds previous two numbers value to compute the next number value. In this program
fibonacci series is calculated using recursion, with seed as 0 and 1. Recursion means a
function calling itself, in the below code fibonacci function calls itself with a lesser value
several times. An termination condition is very important to recursion function, i.e n == 0
and n == 1 or the recursive call would be infinite leading to stack overflow error.
4. C Program to print array in reverse
Algorithm:

1. Input size and elements in an array. Store it in some variable
say size and arr respectively.
2. Declare another array that will store reversed array elements of original array with same
size, say reverse[size].
3. Initialize two variables that will keep track of original and reverse array. Here we will
access original array from last and reverse array from first. Hence, initialize arrIndex =
size - 1 and revIndex = 0.
4. Run loop from size - 1 to 0 in decremented style. The loop structure should look
like while(arrIndex >= 0).
5. Inside loop copy original array to reverse array i.e. reverse [revIndex] = arr[arrIndex];.
6. After copy, increment revIndex and decrement arrIndex.
7. Finally after loop print reverse array.
Code:
#include <stdio.h>
voidmain()
{
int arr[50];
int size,i;
printf("Entersize of the array:");
scanf("%d",&size);
printf("Enterelements inarray:");
for(i=0;i<size;i++)
{
scanf("%d",&arr[i]);
}
printf("nArrayinreverseorder:");
for(i = size-1;i>=0; i--)
{
printf("%dt",arr[i]);
}
}
Discursion:

This algorithm in real does not produces a reversed array. Instead it just prints array in
reverse order. If you are looking to reverse the elements then skip to next logic. So here
goes step by step descriptive logic to print array in reverse order.
a. Input size and elements in array from user. Store it in some variable
say size and arr.
b. Run a loop from size - 1 to 0 in decremented style. The loop structure should look
like for(i=size-1; i>=0; i--).
c. Inside loop print current array element i.e. arr[i].
5. C Program to Merge the Elements of 2 Sorted Array
1. Create two arrays of some fixed size and define their elements in sorted fashion.
2. Take two variables i and j, which will be at the 0th position of these two arrays.
3. Elements will be compared one by one using i and j in for loop, and whichever element is smaller
than the other, that element will get inserted to final array and the position(either i or j) will move by
one, whereas the other array’s track position will remain in that same place.
4. Above work will be done till we reach the end of either array. After that, one of the array whose
elements are still to be added, its elements will get straightaway added to the final array.
#include <stdio.h>
void main()
{
int array1[50], array2[50], array3[100], m, n, i, j, k = 0;
printf("n Enter size of array Array 1: ");
scanf("%d", &m);
printf("n Enter sorted elements of array 1: n");
for (i = 0; i < m; i++)
{
scanf("%d", &array1[i]);
}
printf("n Enter size of array 2: ");
scanf("%d", &n);
printf("n Enter sorted elements of array 2: n");
for (i = 0; i < n; i++)
{
scanf("%d", &array2[i]);
}
i = 0;
j = 0;
while (i < m && j < n)
{
if (array1[i] < array2[j])
{
array3[k] = array1[i];
i++;

}
else
{
array3[k] = array2[j];
j++;
}
k++;
}
if (i >= m)
{
while (j < n)
{
array3[k] = array2[j];
j++;
k++;
}
}
if (j >= n)
{
while (i < m)
{
array3[k] = array1[i];
i++;
k++;
}
}
printf("n After merging: n");
for (i = 0; i < m + n; i++)
{
printf("n%d", array3[i]);
}
}

Discursion:
1. Declare 2 1D arrays of some fixed size, then take size of the arrays from user and define all the
elements of the array according to the size in sorted fashion.
2. Take two variables, i and j as iterators which will track the position of elements in arrays.
3. Running a while loop till we reach the end of either array, the element at ith and jth position of two
arrays are compared.
4. The smaller element gets inserted into final array (third array, whose size is the sum of the size of
these two arrays) and the track position gets incremented by 1.
5. This process continues, till we reach the end of either array.
6. After finishing the loop above, one of the array’s tracker(i.e either i or j) will not be at the last
position of the corresponding array, in that case we will have to add all the remaining elements of
that array to the final array as it is one by one
6. C Program to Check if a String is a Palindrome without using the Built-in Function
Algorithm:
a. Take a string as input and store it in the array.
b. Reverse the string and store it in another array.
c. Compare both the arrays.
#include <stdio.h>
void main()
{
char string[25], reverse_string[25] = {'0'};

int i, length = 0, flag = 0;
printf("Enter a string:");
gets(string);
for (i = 0; string[i] != '0'; i++)
{
length++;
}
for (i = length - 1; i >= 0 ; i--)
{
reverse_string[length - i - 1] = string[i];
}
for (flag = 1, i = 0; i < length ; i++)
{
if (reverse_string[i] != string[i])
flag = 0;
}
if (flag == 1)
printf ("n%s is a palindrome", string);
else
printf("n%s is not a palindrome", string);
}
Discursion:
a. Take a string as input and store it in the array string[].
b. Store the same string into the another array reverse_string[] in the reverse fashion.
c. Using for loop compare the elements of both the arrays.
d. If all the elements of the array are same, then it is a palindrome. Otherwise it is not a palindrome.

Write a program to check a given number is prime or not

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Write a program to check a given number is prime or not