School of Computer Science Introduction to Algorithms and Programming Winter Midterm Examination # 1 Wednesday, February 11, 2015

Transcription

1 Page 1 of 8 School of Computer Science Introduction to Algorithms and Programming Winter 2015 Midterm Examination # 1 Wednesday, February 11, 2015 Marking Exemplar Duration of examination: 75 minutes 1. Answer all questions on this examination paper in the space provided. 2. This is a closed-book examination no notes or books or electronic computing or storage devices may be used. 3. Do not copy from other students or communicate in any way with other students. All questions will be answered only by the attending proctors. 4. All students must remain seated during the last 5 minutes of the examination unless directed otherwise by the attending proctors. 5. The examination must be surrendered immediately when the instructor announces the end of the test period. 6. Each student must sign the examination signature list before leaving the classroom. Total mark obtained: Maximum mark: 45 NOTE: You may use the reverse side of any page to continue an answer to a question, or for rough work. Clearly identify each such continuation by the question number (and part letter if applicable).

2 Page 2 of 8 Question 1. [ 10 marks ] Answer all parts below. For each multiple choice question circle the single response which most correctly completes the question. A. The printf() function is defined through the library. 1) stdlib.h 2) ctype.h 3) stdio.h 4) math.h B. The fabs() function is defined through the library. 1) stdlib.h 2) ctype.h 3) stdio.h 4) math.h C. In order to permit programmers to reference functions defined in libraries, it is necessary to use the directive. 1) #include 2) #define 3) #stdlib.h 4) libscanf() D. What will be output if you will compile and execute the following C language code? #include <stdio.h> #define x 5+2 int main () int i; i = x * x * x ; printf( "%d", i ) ; return 0 ; 1) 343 2) 27 3) 133 4) Compiler error will occur

3 Page 3 of 8 E. What will be output if you will compile and execute the following C language code? #include <stdio.h> int main () int i=3, *p=&i; *p = *p**p ; printf( "%d", i ) ; return 0 ; 1) 9 2) 3 3) 27 4) Run-time error will occur F. What will be output if you will compile and execute the following C language code? #include <stdio.h> #define max 5 int main () int i=0 ; i = max++ ; printf( "%d", i++ ) ; return 0 ; 1) 5 2) 6 3) 7 4) Compiler error will occur G. What will happen if in a C program you assign a value to an array element whose subscript exceeds the size of array? 1) The element will be set to 0 2) The compiler would report an error 3) The program may crash if some important data gets overwritten 4) The array size would appropriately grow

4 Page 4 of 8 H. In C, if you pass an array as an argument to a function, what actually gets passed? 1) Value of elements in array 2) First element of the array 3) Base address of the array 4) Address of the last element of array I. How many times will the program below print "BIX"? #include<stdio.h> int main() printf("bix\n"); main(); return 0; 1) Infinite times 2) ) ) Some large number of times until stack overflow, or segment fault, occurs J. Which of the following is not a C language keyword? 1) auto 2) register 3) static 4) function

5 Page 5 of 8 Question 2. [ 10 marks ] Part A. [ 5 marks ] Write a complete iterative function definition for the function Starline(N), where N is an int type variable. If N is less than or equal to zero, the function does nothing except return. If N is greater than 0, it prints N asterisks ( * ) on a single line, followed by a newline signal. Ex. Starline(1); // Output: * Starline(3); // Output: *** ANSWER: Iterative Version : void Starline ( int N ) int k ; if( N <= 0 ) return ; for( k=n; k>0; k-- ) printf( * ); printf( \n ) ; return ;

6 Page 6 of 8 Question 2 (continued) Part B. [ 5 marks ] Write a complete recursive function definition for the function Reverse(A,S,N), where A is an array of char values (assume the maximum size of A is 100), S is an int which provides the starting subscript of a sub-array within A (S is 0 initially) and N is an int which provides the actual number of characters in A. If N <= 1, Reverse() does nothing except return. However, if N > 1, Reverse() reverses the order of elements in A. Your definition must not contain any I/O statements. Ex. Assume A = c, a, t and N=3. After returning from Reverse( A, 0, N ); A = t, a, c ANSWER: Recursive Version I : void Reverse ( char A[], int S, int N ) char tc ; if( N <= 1 ) return ; tc = A[0] ; A[0] = A[N-1] ; A[N-1] = tc ; Reverse( &A[1], 0, N-2 ) ; return ; Recursive Version II : void Reverse ( char A[], int S, int N ) char tc ; if( N <= 1 ) return ; tc = A[S] ; A[S] = A[N-1] ; A[N-1] = tc ; Reverse( A, S+1, N-2 ) ; return ;

7 Page 7 of 8 Question 3. [ 10 marks ] Write a complete C language function definition called Search(A,N,S), where A is an array of double type values, N is an int type variable that specifies the actual number of values in A, and S is a double type variable. When Search() is called, it performs a search for the value S in A and returns the value of the position (ie. subscript) where S was found; otherwise a value -1 is returned. Assume that all input parameters have been suitably initialized before the function call. Make no further assumptions about the data stored in array A. ANSWER: /* Object: Search a list of double values and return position of found value Input: 1-D array of double, integer number of values, and double search value Output: integer subscript of position where value found, otherwise negative */ int Search ( double A[], int N, double S ) int P = 0 ; // Use for position, init. to start of list // Loop exits when value found at position P, or value // not found in list for( ; P < N && S!= A[P] ; P++ ) ; if( P < N ) return P ; // if value found, return position return -1 ; // otherwise return negative

8 Page 8 of 8 Question 4. [ 15 marks ] Write a complete C language program designed to execute with input and output provided to the file system, using I/O file redirection: a.out < Input.txt > Output.txt. Assume the file Input.txt contains float values, one per line. The number of values in the file is not known in advance, but should be assumed to be from 0 to Your program must input all the values into a suitably defined array, then call a function Sort() that accepts input of a 1-dimensional array of float values and the actual number of values (an int) in the array and then sorts the values in descending (largest to smallest) order before returning. You may use any sorting algorithm to perform the sort. Before exiting the program, the sorted array should be outputted to Output.txt. Since no humans are involved with the program during execution, there is no need to provide user prompts. ANSWER: #include <stdio.h> void Sort ( double A [ ], int N ) ; // Proto: BUBBLE SORT int main ( void ) float A[1000] ; // array must be able to handle 1000 int E, N ; for( N=0 ; (E = scanf( %f, A[N] ))!= EOF ; N++ ) ; Sort( A, N ) ; for( E=0 ; E<N ; E++ ) printf( %f\n, A[E] ) ; return 0 ; void Sort ( double A [ ], int N ) // Defn: BUBBLE SORT int I, J ; double t ; for( I=0; I < N-1; I++ ) for( J=N-1; J > I; J-- ) if( A[J] > A[J-1] ) t = A[J]; A[J] = A[J-1] ; A[J-1] = t ; return ; Proper solutions may also be expressed using other sorting algorithms.