CMPT 130 Sample Final Solution

Transcription

1 CMPT 130 Sample Final Solution Last name exactly as it appears on your student card First name exactly as it appears on your student card Student Number SFU This is a 180 minute test. It is closed book: no calculators, computers, notes, books, etc. are allowed. Question Your mark Out of What's Printed 20 Multiple Choice 5 Memory 7 Fragments 9 Structures 10 Perfect Numbers 8 Binary to Decimal 8 Total Page 1 of 10

2 Question 1: What s Printed? Show what would be printed by each of the statements shown below. int i; for(i = 0; i < 4; ++i) printf("%d ", i+1); The next 7 questions are related to each other int arr1[] = 2,4,6,8,10; int* p = arr1; int s = 0; int* q; printf("\n%d\n", sizeof(arr1)); 1,2,3,4 20 printf("%d\n", sizeof(p)); 4 printf("%d\n", sizeof(*p)); 4 printf("%d\n", *p); 2 printf("%d\n", arr1[3]); 8 for(q = arr1; q < arr1 + 5; s += *q++); printf("%d\n", q-p); 5 printf("%d\n", s); 30 long long yy = 0; int x = 412; printf("%d\n%d\n", yy, x); 0 0 int hex = 163; printf("%x\n", hex); a3 Page 2 of 10

3 The next 8 questions are related to each other char str1[15] = "hades"; char str2[15] = "haddock"; printf("%d\n", sizeof(str1)); 15 printf("%d\n", strlen(str1)); 5 putchar(str1[3]); e printf("\n%d\n", str1[6]); 0 fputs(str2, stdout); if(strncmp(str1, str2, 3) == 0) printf("\nsame\n"); else printf("different\n"); printf(strcat(str1, ", pluto")); haddock same hades, pluto printf("\n%d\n",str1[2] - str1[1]); 3 if(7 < 5 3 && 3!= 4) printf("true\n"); else printf("false\n"); int start = 0; int end = 0; while(start < 100) start++; if(start % 2 == 1) continue; if(start == 8) break; end++; printf("%d\n", end); true 3 Page 3 of 10

4 Question 2: Multiple Choice Which of the following are likely to result in a stack overflow? 1. A recursive function with no base case 2. An infinite loop that does not contain variable declarations 3. Allocating space in automatic memory for many large structures 4. Allocating space in dynamic memory for many large structures a. 1 and 3 b. 1, 2 and 3 c. 1 only d. 1, 2, 3 and 4 Which of the following correctly allocates spaces in dynamic memory for an array of 100 doubles? a. double* p = malloc(100, sizeof(double)); b. double* p = malloc(100 * sizeof(double)); c. double* p = malloc(100 * sizeof(int)); d. double* p = calloc(100 * sizeof(double)); a Which of the following placeholders would be appropriate for displaying right justified, positive floating point numbers less than one million to three decimal places. Assume that a column of such numbers is to be displayed so that they line up. a. "%-6.3f" b. "%6.3f" c. "%-10.3f" d. "%10.3f" What is printed by the call to f shown below? printf("f(5) = %d", f(5)); a. f(5) = 5 b. f(5) = 32 c. nothing, f does not compile d. f(5) = 10 int f(int x) if(x > 1) return 2 * f(x - 1); else if(x == 1) return 2; else return x; Which of the following is the best description of the error in the statements shown below: b d b int arr[] = 1,2,3,4; arr = int[10]; a. The variable arr is declared twice b. An array cannot be initialized with a bracketed list of values c. An array variable must be specified with a constant or a literal d. A previously declared array variable cannot be assigned another array d Page 4 of 10

5 Question 3: Memory #include "stdio.h" #include "stdlib.h" int num = 33; int glob = 42; static int fill = 113; int bar(int* aa, int bb); int main() int i; int num = 10; int x = 100; int* arr = calloc(num, sizeof(int)); for(i = 0; i < num; ++i) int x; x = i * 2; arr[i] = x; printf("%d\n", bar(&num, x)); printf("%d\n", bar(&num, x)); printf("%d, %d\n", bar(&x, x), num); free(arr); return 0; int bar(int* a, int b) static int count = 0; ++(*a); b++; count++; return count; For each variable state the line numbers corresponding to its scope. Example line 05 glob 05 to 38 line 06 fill line 08 aa 08 line 13 num line 14 x 14-16, line 18 x State the variables' storage locations. Select static, automatic or dynamic. line 05 glob line 15 arr static line 15 - data assigned to arr line 33 count line 31 b automatic static automatic dynamic What is printed by the last print statement (line 25)? 3, 10 Is the linkage of fill (line 06) internal or external? internal or external. internal (because of static) Page 5 of 10

6 Question 4: Fragments Complete the program fragment shown to the right by writing a while loop that repeatedly prompts the user to guess a number. The loop should terminate when the guess is equal to the answer. Sample Output Guess the number! 12 Guess the number! 6 Guess the number! 19 Guess the number! 4 Guess the number! 17 Congratulations! Complete the program fragment shown to the right by writing a for loop that prints all of the integers between start and end, with each integer printed on a separate line. If start is greater than end nothing should be printed. Sample Output Enter the start value: -2 Enter the end value: Complete the program fragment shown to the right by writing an if statement that checks to see if the three variables are all equal to each other, all are different, or if just two are equal. Sample Output (3 different executions) Enter three numbers: they are all different Enter three numbers: they are all the same Enter three numbers: only two are the same int answer = rand()%20; int guess = 0; while(answer!= guess) printf("guess the number! "); scanf("%d", &guess); printf("congratulations!\n"); int i, start, end; printf("enter the start value: "); scanf("%d", &start); printf("enter the end value: "); scanf("%d", &end); for(i = start; i <= end; ++i) printf("%+2d\n", i); int x, y, z; printf("enter three numbers: "); scanf("%d%d%d", &x, &y,&z); if(x == y && x == z) printf("they are all the same\n"); else if(x!= y && x!= z && y!= z) printf("they are all different\n"); else printf("only two are the same\n"); Page 6 of 10

7 Question 5: Structures #include "stdio.h" #include "stdlib.h" #define FNAME_LEN 20 #define NAME_LEN 10 #define MAX_AC 10 typedef struct char name[name_len]; float balance; account; account foo(account* pacc, int size); int main() char fname[fname_len]; account bank[max_ac]; FILE* fp; int readresult = 2; int size = 0; account smacc; account test = "bob", ; account* pacc = &test; printf("enter a file name: "); gets(fname); if((fp = fopen(fname, "r")) == NULL) printf("error 1"); exit(1); readresult = fscanf(fp, "%s%f", bank[size].name, &bank[size].balance); if(readresult!= 2) printf("error 2"); exit(1); while(readresult == 2) size++; readresult = fscanf(fp, "%s%f", bank[size].name, &bank[size].balance); printf("%s\n", test.name); printf("%.2f\n", pacc->balance); printf("%s\n", bank[0].name); printf("%c\n", bank->name[0]); account foo(account* pacc, int size) int i; account result = pacc[0]; for(i = 1; i < size; ++i) if(pacc[i].balance < result.balance) result = pacc[i]; return result; smacc = foo(bank, size); printf("name = %s, balance = %.0f\n", smacc.name, smacc.balance); return 0; Page 7 of 10

8 The questions on this page (except the two multiple choice questions) relate to the program shown on page 7. Show what is printed by the program for each of the three input files shown below. Note that there is no file called loans3.txt! contents of loans1.txt Bruce Diana Clark Peter Dinah Bob Sue Kate contents of loans2.txt no file called loans3.txt exists Enter a file name: loans1.txt bob Bruce B name = Peter, balance = 12 Enter a file name: loans2.txt error 2 Enter a file name: loans3.txt error 1 Which of the following statements will open a file called vip.txt without over-writing its data, and allow data to be added to the end of the file, and allow the contents of the file to be read? a. FILE* fp = fopen(fname, "w+"); b. FILE* fp = fopen(fname, "w"); c. FILE* fp = fopen(fname, "a+"); d. FILE* fp = fopen(fname, "w"); Which of the following function calls would write a double array of size 100 (called arr) to a binary file which is pointed to by the file pointer fp? a. fwrite(arr, sizeof(double), 100, fp); b. for(i=0; i < 100; ++i) fwrite(arr[i], sizeof(double), 100, fp); c. for(i=0; i < 100; ++i) fprintf(fp, "%f", arr[i]); d. fread(arr, sizeof(double), 100, fp); c a Page 8 of 10

9 Question 6: Perfect Number A perfect number is a positive number that is equal to the sum of its proper positive divisors (a proper divisor is a positive divisor of a number, excluding the number itself). For example 6 is a perfect number, since its divisors are 3, 2 and 1. Write a function with a single integer parameter that returns 1 if its parameter is a perfect number and 0 if it is not. Examples int isperfect = perfect(6); // isperfect = 1 isperfect = perfect(8); // isperfect = 0 int perfect(int x) int sum = 0; for(int i = 1; i < x; ++i) if(x % i == 0) sum += i; if(sum == x) return 1; else return 0; Page 9 of 10

10 Question 7: Binary to Decimal Write a function that takes a string representation of a binary number and returns the decimal equivalent. Your function should have a single character array parameter and should return an integer. Examples int bin = binarytodecimal("11111"); // bin = 31 bin = binarytodecimal("101010"); // bin = 42 bin = binarytodecimal("-100"); // bin = -4 int binarytodecimal(char bin[]) int result = 0; int power = 1; char ch; for(int i = strlen(bin)-1; i >= 0; i--) if(bin[i] == '1') result += power; power = power * 2; return result; Page 10 of 10