CS 30 Winter 2007 Final Exam. Open books and notes (used in the class). 
No laptops.

Problem 1. 
a) (15 pts) In the program below, what is printed out if the entered
input is 2 4? What about if 1 5 is entered - what might happen? What     
happens if we add another occurrence of block A after block C - what would
the added print out be?















b) (10 pts) Block B and Block C are identical and print out the five names.
However, the order that the names are printed out might not be the same.
Explain how that happens, even though the name array is not changed in  
this program.







c) (10 pts) Write a single function, called printnames to replace Blocks B and C,
and make all other needed changes to the program so that it computes
exactly the same results as before, using printnames in place of Blocks B
and C. You can write printnames here, and make the other needed
changes on the program below. Can that printnames also replace 
Block A? Explain your answer.




















#include<stdio.h>
main()
{

int i, n1, n2;
char * pc[5],  * pt;
char  name[][10] = {"dave", "john", "peter", "yolanda", "henry"};

/*Block A */
for (i = 0; i < 5; i++)
printf("%s\n", name + i);
printf("\n");
/* end of Block A */

for (i = 0; i < 5; i++)
 pc[i] = name[i];

/* Block B */
for (i = 0; i < 5; i++) {
printf("%s\n", pc[i]);
}
printf("\n");
/* end of Block B */

scanf("%d%d", &n1, &n2);

pt = pc[n1];
pc[n1] = pc[n2];
pc[n2] = pt;

/* Block C */
for (i = 0; i < 5; i++) {
printf("%s\n", pc[i]);
}
printf("\n");
/* end of Block C */

}

----------------------------


Problem 2 (25 pts):

NOTE to CS 30 Winter 2008: We didn't cover recursion very extensively
this year, so I would not have as hard a problem as this on recursion
this year. But in case you want to see last year's problem on recursion,
here it is:
 
This problem concerns a recursive program to compute the a number S(n,m),
called the Sterling Number, for two non-negative integers n and m, where n
is larger or equal to m. The recursive formula for S(n,m), where n and m
are both non-negative integers, is S(n,m) = S(n-1, m-1) + m x S(n-1, m).
There are three base cases: S(n,0) = 0 for any n > 0; S(n,m) = 0 if n is  
less than m; S(n,m) = 1 n = m.

Write the program to take in pairs of integers n and m, computing S(n,m)
each time, until the user inputs a negative number for either n or m.  


























-----------------------------

Problem 3: (25 pts)
Suppose S is the string 'abcdefg'. A left-circular shift of S by 3 places
creates the string defgabc. A left-circular shift of S by 5 places creates
the string fgabcde. Write a function called leftshift that is passed S, n
and p and implements a left-circular shift of S by p places. The main
reads in S, finds its string length (you can use a function in string.h 
for that) and calls leftshift. 

Hint: There is a simple relationship between left shift and right shift.
If you can see it quickly, you should be able to quickly modify the right
shift program. However, you can always think through how to do a left
shift from scratch.

Note to CS 30 Winter 2008. In 2007 one of the homework problems was to
write a program to do right shift, so this problem was not as hard for
the 2007 class at it might seem to you, since you have not thought previously
about shifting problems at all.


























---------------------

Problem 4: (25 pts) The following is the start of a program that holds 
the x,y coordinates of the four corners of a number of rectangles. The 
four corners of each rectangle are collected into a struct called (duh!)
rectangle. To be a proper rectangle, the x coordinate of the lower right
corner should be greater than the x coordinate of the upper left corner,
and the y coodinate of the lower right corner should be less than the y
coordinate of the upper left corner. Your task is to complete the program
where the comments say to add code. You must add the code in those locations
of the program. That is, the modifications go there, but if you need more
room to write the answers, use the back of the sheet.


#include<stdio.h>

struct rectangle {
	int UL[2]; /* holds the x,y coordinates of the upper left corner 
                   - the others are similar */
        int UR[2];
	int LL[2];
	int LR[2];
};

main()
{
int i,j, xul, yul, xlr, ylr;
struct rectangle my[10];

for (i = 0; i < 2; i++) { 
printf("input the x,y coordinates of the upper-left corner of a rectangle\n");
scanf("%d%d", &xul, &yul);
my[i].UL[0] = xul;
my[i].UL[1] = yul;

printf("input the x,y coordinates of the \
lower-right corner of the same rectangle\n");

scanf("%d%d", &xlr, &ylr);
my[i].LR[0] = xlr;
my[i].LR[1] = ylr;

/* Put code here to check that the x,y coordinates of the two entered 
corners are in the correct relationship as discussed above. If not,
just print that fact and print out i. */








}

for (i = 0; i < 2; i++) {

/* Put code here to finish filling in the fields for the rectangles in array my. 
Do not ask the user for more input, but rather use the information already input. 
Think about how the x,y coordinates of a rectangle relate to each other, 
and what has already been input */















}

printf("input an index (from 0 to 9) for one of the rectangles\n");
scanf("%d", &i);
printf("The upper right x and y coordinates for rectangle %d are: ", i);
/* Put code here to print out the proper coordinates */






printf("The lower left x and y coordinates for rectangle %d are: ", i);
/* Put code here to print out the proper coordinates */





}
--------------------------------

Problem 5: (25 pts)

The following program is extracted from the program twodarray.c that we
looked at in the class. It is supposed to compute the transpose of an
array. Recall that the transpose of an array changes the rows into columns
and the columns into rows. For example if ar is

1 2 3
4 5 6
then the transpose tr is
1 4
2 5
3 6

The following program works fine when n equals m, and MAXROW equal MAXCOL,
but has problems when either n is not equal to m, or if we change the
definitions so that MAXROW is not equal to MAXCOL.  Explain what those two
problems are, and how to fix the first one.









#include<stdio.h>
#define MAXROW 10
#define MAXCOL 10 

main()
{
int ar[MAXROW][MAXCOL], tr[MAXROW][MAXCOL],n, m, i,j;

        do {
        printf("Enter the number of rows and columns for the array\n");
        scanf("%d%d", &n, &m);
        }
        while (n > MAXROW || m > MAXCOL);

        for (i = 0; i < n; i++) {
		for (j = 0; j < m; j++) {
                  printf("Enter an integer for cell %d, %d \n", i, j);
                  scanf ("%d", &ar[i][j]);
	        }
        }


  /*Here we create the transpose of the array*/
        for (i = 0; i < n; i++) {
		for (j = 0; j < m; j++) {
			tr[j][i] = ar[i][j];
	        }
                printf("\n");
        }

   printf("The transpose of the input array is \n");
        for (i = 0; i < n; i++) {
		for (j = 0; j < m; j++) {
                  printf("%d ", tr[i][j]);
	        }
                printf("\n");
        }

}

------------------------
Problem 6: (25 pts)
In the program below, add the needed code so that the program prints
out the array, but with the order of the columns reversed. 
For example, if the input is 3 4, then the output would be:

0 1 2 3 
1 2 3 4 
2 3 4 5 

3 2 1 0 
4 3 2 1 
5 4 3 2 


#include<stdio.h>
#include<stdlib.h>
main()
{
int i,j, k, n,m ;
int * p;

printf("Input the two dimensions of the dynamically allocated array \n");
scanf("%d%d", &n, &m);

p = malloc(n*m * sizeof(int));

for (i = 0; i < n; i++) {
	for (j = 0; j < m; j++) {
		
        k = i*m + j;
	*(p + k) = i+j; 
        }
}

for (i = 0; i < n; i++) {
	for (j = 0; j < m; j++) {
        k = i*m + j;
       printf("%d ", *(p+k));
        }
    printf("\n");
}
    printf("\n");

/* Add the code here */













}


---------------------

Fake Extra credit problem:

Complete the following sentence: I love C because ______


Note to CS30 Winter 2008. There were some very interesting responses
to this question. You might think about it yourself.