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CTEC1401 Programming in C
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Week 17: Functions II
Week 18: Functions III
 Week 19: Searching

  1. Before the lab session read CFTTP Chapter 11 and study the solved exercises very carefully.

  2. Attempt the followingunsolved exercises at the end of Chapter 11:

    • 11.1, 11.2, 11.4
    • 11.9, 11.10
    • 11.14, 11.15

  3. fact

    Write a program fact.c that asks the user to enter an integer number N. The program then prints out the first N factorial numbers. Remember that fac(1)=1, fac(n)=n*fac(n-1). You should use a function fac that is written recursively.

  4. fibs

    Write a program called fibs.c that contains a recursive function for calculating the nth Fibonacci number. The program should accept a number as a command line argument and then call the Fibonacci function to calculate the corresponding Fibonacci number and then display the result. Recall the definition of the Fibonacci numbers:

    • fib(0) = 1
    • fib(1) = 1
    • fib(n) = fib(n-1) + fib(n-2), when n ≥ 2

  5. recSum

    Write a recursive function: 

    int sum( int x, int max )
{
  /* complete the code */
}
    that calculates the sum of the numbers from x to max (inclusive). For example, sum (4, 7) would compute 4 + 5 + 6 + 7 and return the value 22. The function must be recursive so you are not allowed to use any conventional loop constructs.

    Save your function along with a main program that tests it thoroughly into a file recSum.c. Compile and run the program.

    6. Supplementary Exercises

  6. sumP2

    Write a recursive function: 

    int sumP2( int maxP )
{
  /* complete the code */
}
    that calculates the sum of the powers of two from 0 to maxP (inclusive). For example, sumP2(7) would compute 20 + 21 + 22 + 23 + 24 + 25 + 26 + 27 and return the value 255. The function must be recursive so you are not allowed to use any conventional loop constructs.

    Save your function along with a main program that tests it thoroughly into a file sumP2.c. Compile and run the program.

  7. ackermann

    Consider the following program. You will see that it takes its input values from the command line (rather than asking the user to enter them when the program is running).

    This program demonstrates the use of command line arguments. The atoi function is used to convert a string into an integer value.

    #include <stdio.h>
#include <stdlib.h>

int ack( int m, int n )
{
   /* Complete this function */
}

int main(int argc, char *argv[])
{
    int m, n;
    if(argc!=3)
    {
      printf("Usage: %s m n\n", argv[0]);
      exit(1);
    }
    m = atoi(argv[1]);
    n = atoi(argv[2]);
    printf("ack(%d,%d) = %d\n", m, n, ack(m, n));
    return 0;
}
    1. Copy the program into ackermann.c and complete the definition of the ack function. (Look up the definition of the Ackermann function to see how it works.)
    2. Look at the table of values (on the Ackermann function web page) and check some of your results against this table.
    3. Use the UNIX time command to provide timings for the following experiments. (Add some more experiments of your own). 
          time ack 0 0
    time ack 2 4
    time ack 3 7
    time ack 3 9
    time ack 3 10
      What do you notice?