MIDTERM TEST EESC 2031 Software Tools June 13, Last Name: First Name: Student ID: EECS user name: TIME LIMIT: 110 minutes

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1 MIDTERM TEST EESC 2031 Software Tools June 13, 2017 Last Name: First Name: Student ID: EECS user name: TIME LIMIT: 110 minutes This is a closed-book test. No books and notes are allowed. Extra space for answers can be found at the end of the test booklet. Assume that o size of char is 1 (byte); o size of short integer is 2 (bytes); o size of integer is 4 (bytes); o size of long integer is 8 (bytes); o size of float is 4 (bytes); o size of double is 8 (bytes); Also assume that the size of a pointer is 8 (bytes). Question Value Mark bonus TOTAL bonus Good Luck

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3 Jun 13, 2017 (Tuesday) Name: Student ID: Page 3 of 15 Question 1 (14.5 pts) 1.1 (0.25 pt) For the following code fragment, what is the output of the printf() statement? int x = 9, y = 13, z = 3; printf("z: %d\n", z *= y + x + 2 ); z: (1 pt) What is the output of the printf() statement? int x = 2, y = x << 2; printf("%d %d %d %d\n", x, y, x y, x&y); (1 pt) What is the output of the printf() statement? int x = 13, y = z = 10; y = x++; z += y++; printf("x:%d y:%d z:%d\n", x,y,z); (1 pt) What is the output of the printf() statement? int x = 3; int y = 4; printf("%d %d %d %d\n", x y, x & y, x y, x && y); 1.5 (0.5 pt) What is the output of the printf() statement? int a = 6; int c = 4; float d = 1.1; short s =1; printf("x:%.3f y:%.3f\n", s*a/c*d, d/c*a*s); (0.5 pt) In 1.5, when d/c*a*s is evaluated, how many type conversions are performed? What is the type of the expression? three float 1.7 (0.5 pt) Recall that in ANSI-C, implicit type conversions are preformed on the following occasions 1) When the operands in an arithmetic or logical expression don t have the same type. 2) When the type of the expression on the right side of an assignment doesn t match the type of the variable on the left side.

4 3) When the type of an argument in a function call doesn t match the type of the corresponding parameter. 4) When the type of the expression in a return statement doesn t match the function s return type. On which of the above occasion(s), is type promotion performed, in which the type of the operand with the narrower type is converted to the type of the other operand? a. On 1) b. On 2) c. On 3) and 4) d. All of the above. 1.8 (1.5 pt) Consider the following ANSI-C program, where the programmer made typos on line 6 and 8, and also missed a else on line 8 #include <stdio.h> int main (){ int in; printf("enter an integer: "); scanf ("%d", &in); if (in = 1) /* this is line 6 */ printf("entered one\n"); if (in = 2) /* this is line 8 */ printf("entered two\n"); else printf("entered others\n"); return 0; What happens when you try to compile and run the program with input 2? (chose a. or b.) a. The program does not compile, because b. The program compiles, output is Entered one Entered two What happens when you try to compile and run the program with input 36? (chose a. or b.) a. The program does not compile b. The program compiles, output is Entered one Entered two What happens when you try to compile and run the program with input 1? (chose a. or b.) a. The program does not compile b. The program compiles, output is Entered one Entered two

5 Jun 13, 2017 (Tuesday) Name: Student ID: Page 5 of (0.25pt) Recall that a gcc compilation process contains three stages. The correct order is a. Linking Pre-processing Compiling b. Pre-processing Compiling Linking c. Compiling Pre-processing Linking d. None of the above 1.10 (1.5 pt) Consider the following statements. For each of the statements, if the right hand side of = is a valid integer literal in ANSI-C, then specify the decimal value of x. If the right hand side of = is not a valid integer literal, specify invalid. int x = b ; invalid int x = 014; int x = 0X3f; 63 int x = 032L; int x = 0xfFG; invalid int x = 0392; invalid 1.11 (3.75 pt) Suppose flags is an integer variable with some value. What happens to flags in each of the following 3 statements, in terms of turning on/off or keeping the bits of flags? Denote the right-most bit as bit 0, the 2 nd right-most bit as bit 1 1) flags = flags (1 << 6); turn on bit 6 (right most is bit 0), keep other bits 2) flags = flags ~(1 << 4); keep bit 4, turn on all other bits 3) flags = flags & 0177; keep right-most 7 bits, turn off all other bits In statement 1) and 2) above, can any of the parentheses be removed without affecting the meaning and value of the expression? If yes, specify which one(s) and briefly explain why. parenthesis in 1) can be removed. Because << has higher precedence than, so 1 << 6 is evaluated before anyway Now suppose you need an int mask whose binary representation is How do you declare it in ANSI-C code? List 3 ways of doing it. int mask = 41 int mask = 051 int mask = 0x29 Other slu: int mask = 1 <<5 1 << 3 1 int mask = 9 1 << 3 anything evaluated to 41 decimal What happens to flags in the following two statements, in terms of turning on/off or keeping bits of flags? Denote the right-most bit as bit 0, the 2 nd right-most as bit 1... flags = flags mask turn on bits 0, 3, 5, keep others flags = flags & mask keep bit 0, 3, 5, turn off all other bits

6 1.12 (1.25 pt) For each of the following array declaration and initializations, determine if the statement is legal in ANSI C. If it is illegal, write illegal. If it is legal, then list (the value of) all the elements in the array, separated by comma or space. int k[3] ={1,5,3,2,25; illegal int k[5] = {1; int k[6] = {1,4,5; int k[] ={1,5,3,2,25; int k2[] = k; illegal 1.13 (1.5 pt) Given the statement char messages[3][20] = {"Hello", "Hi", "There"; What is the value of sizeof(messages)? 3 * 20 * 1 = 60 (bytes) write a single C statement to change "Hi" to "How are you" strcpy (messages[1], How are you ) or sprintf(messages[1], %s, How are you ) or sprintf(messages[1], How are you ) write a single C statement to change 'h' in "There" to 'H' messages [2][1] = H or messages[2][1] =toupper(messages[2][1]); Question 2 (12 pt) 2.1 (1 pt) Consider the following ANSI C program. #include<stdio.h> void afunction (float input){ input = input * 2.0; int main(){ float input; scanf("%f", &input); afunction(input); printf("%.3f\n", input); Now suppose the program compiles and the user enters 7.4 What is the output of the program? Call by value. The formal argument of function happens to have the same name as the actual argument but they are two variables. The former is a copy of the latter.

7 Jun 13, 2017 (Tuesday) Name: Student ID: Page 7 of (1 pt) Consider the following function definition in ANSI C. /* this function initializes argument array arr s first n elements to 0 */ void cleararr (int arr[], int n){ int index; while (index < n){ arr[index++] = 0; Do you think that this function will work as expected? Yes No. The reason is: index is a local variable, which is initialized by the compiler to a garbage value, not 0 need to initialize to 0 explicitly. 2.3 (1pt) Consider the following ANSI C program. #include<stdio.h> #define N 4 void afun(); int main(int argc, char *argv[]) { int k; for(k=0; k<n; k++) afun(); return 0; void afun(){ int static counter; int y = ++counter; printf("%d ", y); What are the outputs of the program? (1 pt) Describe the usage(s) of key word static for global variable in ANSI-C. Limit the scope to the file in which it is defined. That is, make it not accessible to the other files.

8 2.5 (2pt) Consider the following ANSI C program. #define N 4 #define INCRE(x) x * x * x #define DECRE(x) x / 2 int main(){ When you invoke the pre-processor, using gcc -E, what is the pre-processed code of main, i.e., the output generated by the preprocessor (and sent as input to the compiler)? /* use marcos */ int i = N + 6; int j = DECRE(i); int k = INCRE(j + 10); int main(){ int i = 4 + 6; int j = i / 2; int k = j + 10 * j + 10 * j + 10 Now we compile and run the program. At the end of main, what is the value of i, j and k? i: 10 j: 5 k: (1.5pt) What are the outputs of the 2 printf() statements in the following code fragment? char msg [] = "Hello"; printf("%d %d", sizeof(msg), strlen(msg)); char msg2[10] = "Hello"; printf("%d %d", sizeof(msg2), strlen(msg2)); (1.5pt) What are the outputs of the 2 printf() statements in the following code fragment? char msg [] = "Hello the world"; printf("%s %d %d", msg, sizeof(msg), strlen(msg)); strcpy(msg, "Hi"); Hello the world printf("%s %d %d", msg, sizeof(msg), strlen(msg)); Hi 16 2

9 Jun 13, 2017 (Tuesday) Name: Student ID: Page 9 of (3 pt) Consider the following ANSI C program. int main(){ char name[60]; int age; float wage; printf("enter name, age and wage: "); scanf("%s %d %f", name, &age, &wage); Explain briefly: printf("%s %d %f", name, age, wage); Briefly explain: Why does function scanf() require the use of & for age and wage (i.e., &age and &wage)? (FYI: if you use age and wage without &,you get segmentation fault and the program crashes.) Scanf needs to change the value of its parameter. Since c is call/pass by value, to change/set the value of age and wage, scanf needs the address/pointer of the variables, and thus &age, &wage. Why don t we need to use & for name in scanf()? (FYI: the program won t compile if you use &name.) In C, array name contains the address of the first elements arr=&arr[0]. So we just pass it to the function without & (actually it is wrong to pass & for arrays) Why don t we need & for age and wage in printf()? To output the values of age and wage (rather than changing them), pass-by-value is sufficient. Just get a copy of the values of age and wage and output them. Question 3 Pointers and arrays ( pt) 3.1 (4 pt) Compete the following program so that the output of main is a: 600 b:18. That is, values of a and b are swapped and then the swapped values are doubled.

10 /* This function double the pointee of arguments, and then call another function to swap the (doubled) values */ void increswap(int *px, int *py) { /* double the values of pointees of px and py */ * px *=2; * py *=2; /* now call function swap() to swap the pointees. swap( px, py ); /* this function swap the pointees of the two pointers */ void swap ( int *p1, int *p2 ) { int tmp = *p1; *p1 = *p2; *p2 = tmp; void main( ) { int a=9, b=300; increswap( &a, &b ); printf("a:%d b:%d", a, b); /* should get a:600 b:18 */ 3.2 (2 pt) What is the output of the following ANSI C program? #include<stdio.h> main(){ What are the two types of testing method and what are the main differences? int x = 199, y = 22; int *ip, *ip2,**pip; ip = &x; pip = &ip; ip2 = ip; y = **pip; (*ip2) *= 10; ip = &y; (** pip)++; (*ip2) -= 10; printf("x:%d y:%d\n", x,y); x: 1980 y: 200

11 Jun 13, 2017 (Tuesday) Name: Student ID: Page 11 of (1.5 pt) Consider the following ANSI C code fragment. int arr [] = {1,2,3,4,5,6; int * p = arr; int i = arr[3]; In addition to arr[3], what are the other ways to access the same element of arr? List 3 ways. int i = *(p + 3) int i = * (arr + 3) int i = p[3] 3.4 (2.25 pt) Consider the following ANSI C program. main(){ int i; int * pint = &i; char c; char * pchar = &c; double d; double * pdouble= &d; printf("%p %p %p\n", pchar, pint, pdouble); /* line 4 */ printf("%p %p %p\n", pchar+1, pint+1, pdouble+1); /* line 5 */ pint++; pchar++; pdouble++; printf("%p %p %p\n", pchar, pint, pdouble); /* line 7 */ pint += 4; pchar += 4; pdouble +=4; printf("%p %p %p\n", pchar, pint, pdouble); /* line 9 */ Suppose the output of the first printf (line 4) is (Recall that printing a pointer directly with %p outputs the content/value of the pointer, which is the address of its pointee, in Hex. To simplify, here we assume it prints in decimal) What is the output of the second printf (line 5)? What is the output of the third printf (line 7)? What is the output of the fourth printf (line 9)?

12 3.5 (2.5 pt) Given the following declaration statements in ANSI C, int arr[]={1,2,3,4,5,6; int * ptr = arr; int i; Specify if each line of (independent) statement below is valid or invalid int * ptr = arr + 3; valid invalid int * ptr = &arr[0] valid invalid i = ptr arr; valid invalid i = ptr + arr; valid invalid i = * (ptr + 2); valid invalid arr++; valid invalid *(arr + 4)=2; valid invalid ptr ++; valid invalid ptr --; valid invalid i = ptr > arr; valid invalid 3.6 (6 pt) Given the following ANSI C program, and assume that the first element of arr is stored in memory address 2000; What is the output of each printf( ) statement? (Recall that %p is used to print the content/value of the pointer, which is the address of its pointee. Here we assume it prints in decimal) main() { int arr[] = {17, 3, 58, 10, 126, 22, 35, 140, 165, 190; int *p = arr; int *q; printf("%p %p %d\n", arr, p, *p); printf("%p %d\n", p+4,*(p+4) ); p; printf("%p %d\n", p, *p); p = arr + 5; printf("%p %d\n", p, *(p + 2)); q = p; p = q +3; printf ("%p %p %d %d %d\n", p, q, p-q, *p, *q); (*p)++; printf("%d %d\n", *(arr+4), *(arr + 8) );

13 Jun 13, 2017 (Tuesday) Name: Student ID: Page 13 of (1.5 pt) For a function that expects a char array as its argument, its prototype can be either void processarr (char []) or void processarr (char *). True False Assume the following ANSI C code fragment int main(){ char msg[] = "Hello the World"; char * p = msg; processarr ( ); /* line 4 */ void processarr (char []){. Which of the following could be a valid function call to processarr in line 4 a. proceeearr(&msg[2]); b. processarr(p); c. processarr(&p[0]); d. processarr(msg+3); e. All of the above 3.8 (2.5+1 bonus) Consider the following ANSI C code, assume that the first element of msg has starting address 1000; what are the outputs of the three printf statements? Recall that %p prints the content of a pointer variable, and here we assume it prints in decimal. main(){ char msg[] = "HelloWorld"; printf("%s %p %d %d\n", msg, msg, sizeof(msg), strlen(msg)); processarray(msg); HelloWorld processarray2(msg); void processarray (char c []){ printf("%s %p %d %d\n", c, c, sizeof(c), strlen(c)); HelloWorld void processarray2 (char * c){ printf("%s %p %d %d\n", c, c, sizeof(c), strlen(c)); HelloWorld

14 3.9 (1.25pt) Consider the following ANSI C program. int main(){ int a[]={2,4,6, 8,10; int resu = dosthrecursively(a, 5); printf("%d\n", resu); return 0; int dosthrecursively(int* c, int n){ if (n==1) return *c; else return *c + dosthrecursively(c+1, n-1); What is the output of the first printf() in main(), or, explain what does function dosthrecursively intend to do? Sum up first n elements in the array c = (0.5 pt Bonus) As mentioned in the textbook and class, the declaration of a pointer related variable is intended as a mnemonic (means help you memorize ). For example, declaration int * ptr; can be interpreted as "expression * ptr is an int (and thus ptr is an integer pointer). Based on this rule, guess what the following statements declare. That is, what is the type that ptr is declared to be? You can draw pictures if you like. (We will talk about this next week in class.) int * ptr []; ptr is an array. Each element of the array is a pointer to integer. That is, ptr is an array of (int) pointers ptr int int * ptr [3] (END of TEST)

15 Jun 13, 2017 (Tuesday) Name: Student ID: Page 15 of 15 Operator precedence (from high to low) and associativity. (You can detach this page, and use it for scratch work )