1- #include <stdio.h>
1+ /**
2+ * @file
3+ * @brief Program to print the nth term of the Fibonacci series.
4+ * @details
5+ * Fibonacci series generally starts from 0 and 1. Every next term in
6+ * the series is equal to the sum of the two preceding terms.
7+ * For further info: https://en.wikipedia.org/wiki/Fibonacci_sequence
8+ *
9+ * @author [Luiz Carlos Aguiar C](https://github.com/IKuuhakuI)
10+ * @author [Niranjan](https://github.com/niranjank2022)
11+ */
212
3- // Fibonnacci function
4- int fib (int number )
13+ #include <assert.h> /// for assert()
14+ #include <errno.h> /// for errno - to determine whether there is an error while using strtol()
15+ #include <stdio.h> /// for input, output
16+ #include <stdlib.h> /// for exit() - to exit the program
17+ #include <time.h> /// to calculate time taken by fib()
18+ /**
19+ * @brief Determines the nth Fibonacci term
20+ * @param number - n in "nth term" and it can't be negative as well as zero
21+ * @return nth term in unsigned type
22+ * @warning
23+ * Only till 47th and 48th fibonacci element can be stored in `int` and
24+ * `unsigned int` respectively (takes more than 20 seconds to print)
25+ */
26+ unsigned int fib (int number )
527{
6- if (number == 1 || number == 2 )
28+ // Check for negative integers
29+ if (number <= 0 )
30+ {
31+ fprintf (stderr , "Illegal Argument Is Passed!\n" );
32+ exit (EXIT_FAILURE );
33+ }
34+
35+ // Base conditions
36+ if (number == 1 )
37+ return 0 ;
38+
39+ if (number == 2 )
740 return 1 ;
8- else
9- return fib (number - 1 ) + fib (number - 2 );
41+
42+ // Recursive call to the function
43+ return fib (number - 1 ) + fib (number - 2 );
1044}
1145
46+ /**
47+ * @brief Get the input from the user
48+ * @return valid argument to the fibonacci function
49+ */
50+ int getInput (void )
51+ {
52+ int num , excess_len ;
53+ char buffer [3 ], * endPtr ;
54+
55+ while (1 )
56+ { // Repeat until a valid number is entered
57+ printf ("Please enter a valid number:" );
58+ fgets (buffer , 3 , stdin ); // Inputs the value from user
59+
60+ excess_len = 0 ;
61+ if (!(buffer [0 ] == '\n' ||
62+ buffer [1 ] == '\n' ||
63+ buffer [2 ] == '\n' )) {
64+ while (getchar () != '\n' ) excess_len ++ ;
65+ }
66+
67+ num = strtol (buffer , & endPtr ,
68+ 10 ); // Attempts to convert the string to integer
69+
70+ // Checking the input
71+ if ( // The number is too large
72+ (excess_len > 0 || num > 48 ) ||
73+ // Characters other than digits are included in the input
74+ (* endPtr != '\0' && * endPtr != '\n' ) ||
75+ // No characters are entered
76+ endPtr == buffer )
77+ {
78+ continue ;
79+ }
80+
81+ break ;
82+ }
83+
84+ printf ("\nEntered digit: %d (it might take sometime)\n" , num );
85+ return num ;
86+ }
87+
88+ /**
89+ * @brief self-test implementation
90+ * @return void
91+ */
92+ static void test ()
93+ {
94+ assert (fib (5 ) == 3 );
95+ assert (fib (2 ) == 1 );
96+ assert (fib (9 ) == 21 );
97+ }
98+
99+ /**
100+ * @brief Main function
101+ * @return 0 on exit
102+ */
12103int main ()
13104{
14- int number ;
105+ // Performing the test
106+ test ();
107+ printf ("Tests passed...\n" );
15108
16- // Asks for the number that is in n position in Fibonnacci sequence
17- printf ("Number: " );
18- scanf ("%d" , & number );
109+ // Getting n
110+ printf (
111+ "Enter n to find nth fibonacci element...\n"
112+ "Note: You would be asked to enter input until valid number ( less "
113+ "than or equal to 48 ) is entered.\n" );
19114
20- printf ("%d \n" , fib (number ));
115+ int number = getInput ();
116+ clock_t start , end ;
21117
118+ start = clock ();
119+ printf ("Fibonacci element %d is %u " , number , fib (number ));
120+ end = clock ();
121+
122+ printf ("in %.3f seconds.\n" , ((double )(end - start )) / CLOCKS_PER_SEC );
22123 return 0 ;
23- }
124+ }
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