chore(C): add odd or even number (#719)

Co-authored-by: LuigiAltamura <luigi.altamura@mail.polimi.it>

algorithms/C/README.md

@@ -34,6 +34,7 @@
 
 - [Palindrome Number](maths/palindrome.c)
 - [Fibonacci Series](maths/fibonacci-series.c)
+- [Odd or Even Number](maths/odd-or-even-number.c)
 
 ## Queues
 

algorithms/C/maths/odd-or-even-number.c

@@ -0,0 +1,32 @@
+/**
+     *This program checks if a number is odd or even.
+     * 
+     * Odd numbers are whole numbers that cannot be divided exactly by 2. If the number is not divisible by 2 entirely, 
+     * it'll leave a remainder 1.
+     * Even numbers are whole numbers that can be divided exactly by 2. If we divide the number by 2, it'll leave a remander 0.
+     * 
+     * Complexity -> O(1)
+     *    _______________________________
+     *   | INPUT | OUTPUT                |
+     *   |   2   | It's an even number!  |
+     *   |   1   | It's an odd number!   |
+     *   |   3   | It's an odd number!   |
+     *    _______________________________
+* */
+
+#include <stdio.h>
+
+int main()
+{
+    int n;
+    printf("Enter a number:\n");
+    scanf("%d", &n);
+    
+    if(n % 2 == 0 ){
+        printf("It's an even number!");
+    }else{
+        printf("It's an odd number!");
+    }
+
+    return 0;
+}