of Fundamentals Computer Science Using C
Midterm for V22.0380, section 1 Spring 1999 8:30 9:45 a.m. March 10, 1999 Instructor: Dilshad M. Shahid
Name: _____________________________________ Student ID: _________________________________
About the exam: Please read 1. This is a closed book exam. 2. You have the entire period to complete the exam. 3. Please keep your eyes on your own paper; cheating with be dealt with severely. 4. Please put all answers directly in the exam itself. The booklets are for scratch work only, and will not be collected or graded.
Name: _____________________________________
I.
True/False Questions (10 Points)
1 Point Each 1. Each C program must have one main function. TRUE 2. Reading a value from memory destroys that value in memory. FALSE 3. b-- means to decrement b by 1 and then use the new value of b in the expression in which b resides. FALSE 4. The expression w - x y*z = 11 where w = 4, x = 5, y = 2 and z = 6.
FALSE
5. A multiple if/else statement can always be rewritten as a switch statement. FALSE
6.
A variable of storage class static exists throughout the execution of the program in which it is declared. TRUE When a function returns a void, a return statement at the end of the function is required. FALSE (refer to pg 155, 1st paragraph) When a function call is encountered, program control remains with main() FALSE
7.
8.
9. The return statement must be the last statement in a function. TRUE 10. Declarations can appear anywhere in the body of a function FALSE
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Name: _____________________________________
II.
Find the Bug Problems (10 Points)
Note: There is only one bug in each of the programs below.
1.
What's wrong with this code? int sum_of_digits(void) { int sum=0; int value = 30; While(value > 15){ sum += 2; value = value/10; } return value; }
The while keyword should be all in lowercase - C is case sensitive
2.
What's wrong with this code? main() { int a=4; int b=2; if( a > = b) printf("a is greater than or equal to b"); } There is a space between > and = . This will give a compilation error.
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Name: _____________________________________
III.
Determine the Output (20 Points)
1. What is the output of the following program:
#include <stdio.h> void draw_shape(int val); main() { int x = 2; int y = 3; draw_shape(x); draw_shape(y); } void draw_shape(int val) { int i, j; switch(val) { case 1: for(i=0; i < 6; i++) { printf("*"); } for(j=0; j < 3; j++) { printf("\n*\n"); } break; case 2: for(i=0; i < 3; i++) { printf("\n*\n"); } for(j=0; j < 6; j++) { printf("*"); } break; default: printf("???***"); break; } /* end of switch statement */ } /* end of function */
4 \n \n \n * * * ******???***
Name: _____________________________________
2. What is the output of the following program: #include <stdio.h> main() { int k; int m; float price1 = 4.5; float price2 = 4.0; while (price2 < price1) { printf("The price is "); printf("%.3f\n", price2); price2 += 1.0; } for(k=0; k < 3; k++) { printf("\nThe price is now...\n"); for(m=1; m < 3; m++) { price2 += 1.0; printf("price = $ %.2f\n", price2); } } } Note: In your answer, please clearly show where the new lines, if any, would occur.
The price is 4.000 n\ The price is now... price = $ 6.00 price = $ 7.00 The price is now... price = $ 8.00 price = $ 9.00 The price is now... price = $ 10.00 price = $ 11.00
n\
n\
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Name: _____________________________________
IV. Short Answer Questions (30 Points)
Each question is 5 points each.
1. What are the four storage class specifiers in C? These can be split into two storage durations: name and define these durations. The 4 storage class specifiers in C are: auto, register, static and extern The two storage durations are: automatic storage duration and static storage duration. Variables with automatic storage duration are created when the block in which they are declared is entered, they exist while the block is active and they are destroyed when the block is exited. Variables of static storage duration exist from the point at which the program begins execution.
2. What do we mean by operator precedence and associativity of the operators? Please give an example demonstrating these two concepts. C evaluates arithmetic expressions in a precise sequence and this sequence is determined by rules of operator precedence. Operator precedence determines, for example, whether a calculation involving a * should be evaluated before one involving a +. Associativity refers to the direction in which evaluation proceeds (left to right or right to left). For example, for the +, - *, / operators, associativity goes from left to right whereas for the =, associativity goes from right to left.
3.
In what situation do we need to use a while loop instead of a for loop? Can all while loops be rewritten as for loops? We use while loops when we do not know in advance how many times we want to loop through the statements contained the inside loop. No not all while loops can be rewritten as for loops.
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Name: _____________________________________
4. Given: main() { int a = 2; int b = 4; int c = 7; b %= a; c *= b; a -= c; printf("%d, %d, %d", a, b, c); } What values of a, b and c would appear on the screen? a is 2, b is 0, c is 0
5.
When you want to use rand() and srand in a program, what header file do you need in addition to <stdio.h> ? Why do you need this extra header file?
You need stdlib.h. You need this extra header file because it contains the function prototypes for rand() and srand and also RAND_MAX which is a constant used by rand().
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Name: _____________________________________
6. Here is a switch statement: int a; switch(a) { case 10: printf("a is has a value\n"); break; case 6: case 2: printf("guess the value\n"); break; default: printf("who knows?\n"); break; } Rewrite this as an if/else statement.
if (a == 10) { printf("a is has a value\n"); } else if(a == 6 || a == 2){ printf("guess the value\n"); } else { printf("who knows?\n"); }
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Name: _____________________________________
V. Write the Function (20 Points)
For the following questions just give the function itself. You do not need to write a complete program. Everything asked for in the question can be contained in one function.
1. Tell Your Fortune. Write a function that predicts a user's fortune! Ask the user to input any positive unsigned integer number (the "silver") and then use this number to randomly come up with a soothsaying. Use the "silver" as a seed to srand() and then use rand() to come up with a numerical "fortune". Your function should have 5 choices for a soothsaying. Use the value of the fortune to pick a soothsaying (e.g. "You will make lots of money" or "You will win a free vacation") and print it out to the screen. At the end return the value of fortune. Here's a hint. The function prototype is: int soothsaying (void); Here's another hint. Declare "silver" as: unsigned silver;
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Name: _____________________________________
Write your function:
int soothsaying (void) { unsigned silver; int fortune; printf("Cross my palm with silver - please input a whole number: "); scanf("%u", &silver); srand(silver); fortune = 1 + rand() % 5; switch(fortune) { case 1: printf("You will get an A in this course\n"); break; case 2: printf("You will find love soon\n"); break; case 3: printf("You will win a BMW\n"); break; case 4: printf("You will be happy all of your days\n"); break; case 5: printf("You will become famous\n"); break; } return fortune; }
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Name: _____________________________________
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Name: _____________________________________
VI. Paragraph/Essay Questions (10 Points)
Please answer 1 OR 2 (not both). Please keep your answers brief.
1.
What does a standard header file contain? Please give 3 example...