April 1999
CA208: 'C' PROGRAMMING

QUESTION 2

Total Marks: 20 Marks

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GRADE A
Sample student's solutions are indicated in green.
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(a) (i) Define what is meant by a recursive function or procedure. [2]
(ii) Define what is meant by an iterative function or procedure. [2]
(i) Recursive function is a kind of function that can call itself  until the condition is met.

(ii) Iterative function or procedure is a kind of function that have a loop that using while loop or for loop and the loop will stop until a condition is met.

 
(b) Assume the following output:

Downwards: 0 of 3
Downwards: 1 of 3
Downwards: 2 of 3
Downwards: 3 of 3
Upwards: 3 of 3
Upwards: 2 of 3
Upwards: 1 of 3
Upwards: 0 of 3

 
(i) Using while loops, write an iterative definition of the procedure levels, that takes two integer arguments, such that a call to levels(4, 3) produces nothing and a call to levels(0, 3) produces the output above. [4]
(ii) Write a recursive definition of the procedure levels, that takes two integer arguments, such that an initial call to levels(4, 3) produces nothing and a call to levels(0, 3) produces the output above. [4]
(i)

void levels (int a , int b)
{
int d; d=a;
while (d<=b)

{
printf ("Downwards : %d of %d", d, b);
d++;
}

d=d-1;
while (d>=0)
{
print ("Upwards : %d of %d", d, b);
d--;
}

}

(ii)

void levels (int a, int b)
{
if (b>=a)

{
printf("Downwards : %d of % d", a, b);
levels (a+1, b);
printf( "Upwards : %d of % d", a, b);
}

}

 
(c) Assume the following function, which is intended to return a range of values depending on the contents of the string mystring:

int foobar(char* mystring) {
    switch(mystring) {
    case("hello"): return 1;
    case("world"): return 2;
    default: return 0;
    }
    return -1;
}

 
(i) Explain why this function is incorrect? [1]
(ii) Identify a construct which would be more suitable for achieving the desired functionality, and explain why this is the case. [2]
(i) The argument to the switch statement should be an Integral type, such as an integer.

(ii) The strcmp is more suitable for achieving the desired functionally because strcmp can compare string mystring with other string with correctly.

 
(d) Given the following procedure:

void foobar(int state, int signal, int timeout) {
   switch (state) {
       case 1:
           if (signal) goto makerunnable;
           if (timeout > 0) {
               timeout = 0;
               printf("Wakeup task\n");
       makerunnable;
               printf("Restarting task\n");
               break;
           }

       default:
       printf("Delete task\n");

       case 2:
       printf("Running task\n");
   }
}

trace the following calls, and produce their output:

 
(i) foobar(2, 0, 0); [1]
(ii) foobar(1, 1, 0); [1]
(iii) foobar(1, 0, 10); [1]
(iv) foobar(3, 0, 10); [1]
(v) foobar(2, 1, 10); [1]
(i) Running task

(ii) Restarting task

(iii) Wakeup task
      Restarting task

(iv) Delete task
      Running task

(v) Running task