In this article, we will write a C program to calculate and print the value of nCr. The formula of nCr is: nCr = n! / ( r!(n - r)! ). For 0 <= r <= n. Here ! represents factorial. For example: 6C2 = 6! / (2! * (6-2)!) => 720/(2 * 24) => 15.
C Program to print the value of nCr based on user input
In this program, we have defined two functions. The factorial() function is to calculate the factorial, which is required in the nCr formula. The second function nCr() is to calculate the value of nCr, this would use the factorial() function.
#include <stdio.h>
/* This function calculates the factorial
* of the passed number n and returns it
*/
unsigned long long factorial(int n) {
unsigned long long fact = 1;
// Loop to calculate the factorial of n
for (int i = 1; i <= n; ++i) {
fact *= i;
}
return fact;
}
// Function to calculate nCr
unsigned long long nCr(int n, int r) {
// If r is greater than n, nCr is 0
if (r > n) return 0;
// Calculate nCr using the formula: nCr = n! / (r! * (n-r)!)
return factorial(n) / (factorial(r) * factorial(n - r));
}
int main() {
int n, r;
// Prompt user to enter the values of n and r
printf("Enter value of n: ");
scanf("%d", &n); //store the entered value in n
printf("Enter value of r: ");
scanf("%d", &r); //store the entered value in r
// Calculate nCr by calling the function
unsigned long long result = nCr(n, r);
// Print the value of nCr for entered values of n and r
printf("%dC%d = %llu\n", n, r, result);
return 0;
}
Output:
Output 1: when value of n is greater than r
Enter value of n: 5
Enter value of r: 2
5C2 = 10
Output 2: when value of r is 0
Enter value of n: 6
Enter value of r: 0
6C0 = 1
Output 3: when value of n and r are same
Enter value of n: 7
Enter value of r: 7
7C7 = 1
Output 4: when value of r is greater than n
Enter value of n: 8
Enter value of r: 9
8C9 = 0
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