*C Program to count prime numbers and display them*

Write a C Program to count prime numbers and display them in descending order using recursion. Here’s simple Program to count prime numbers and display them in descending order using recursion in C Programming Language.

**Recursion : :**

**Recursion : :**

- Recursion is the process of repeating items in a self-similar way. In programming languages, if a program allows you to call a function inside the same function, then it is called a
of the function.**recursive call**

- The C programming language supports recursion, i.e., a function to call itself. But while using recursion, programmers need to be careful to define an exit condition from the function, otherwise it will go into an infinite loop.

- Recursive functions are very useful to solve many mathematical problems, such as calculating the factorial of a number, generating Fibonacci series, etc.

Below is the source code for C Program to count prime numbers and display them in descending order using recursion which is successfully compiled and run on Windows System to produce desired output as shown below :

**SOURCE CODE : :**

**SOURCE CODE : :**

/* C Program to count prime numbers and display them in descending order using recursion */ #include<stdio.h> #include<math.h> int countPrimes(int a, int b); int isprime(int n); int main() { int a,b; printf("Enter values of a and b :"); scanf("%d %d",&a,&b); printf("\n\nTotal prime numbers = %d\n",countPrimes(a,b)); return 0; } countPrimes(int a, int b) { if(a>b) return 0; if(isprime(b)) { printf("%d ",b); return 1 + countPrimes(a,b-1); } else return countPrimes(a,b-1); } int isprime( int n) { int i; for(i=2; i<=sqrt(n); i++) if(n%i == 0) return 0; return 1; }

**OUTPUT : :**

**OUTPUT : :**

***************OUTPUT*************** ***************FIRST RUN************ Enter values of a and b : 2 100 97 89 83 79 73 71 67 61 59 53 47 43 41 37 31 29 23 19 17 13 11 7 5 3 2 Total prime numbers = 25 ***************SECOND RUN************ Enter values of a and b : 5 50 47 43 41 37 31 29 23 19 17 13 11 7 5 Total prime numbers = 13

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