Study Guide 1

Quizzes will be closed book. 30 minutes in lab.

Topics:

Programming in C
Data types and sizes
UNIX commands
Function stacks
Basic arrays

Write C programs to check your answers. Or you can ask a TA or instructor to give feedback on your responses.

Practice questions

1) What is the minimum size of the following structures?

struct Snack {
  char name[32];
  int quantity;
  float cost;
};

Hint: To check your answers, use the sizeof() function.

2) Consider navigating directories from the command prompt in UNIX. Suppose you are in your home directory.

How would you create a subdirectory with name foo?
How would you see the contents of your .bashrc file?
How would you list the contents of foo?
How can you create a file in the directory foo called test.c?
How can you compile a c program?

3) Suppose Willa is in their home directory, /home/willa. Write commands to produce the following directory structure. Willa contains two sub-directories, A ad B, and one file hello.c. B contains a sub-directory C and file test.txt. Below is a visualization of it where child directories are indented.

\home\willa
  A
  B
    C
    test.txt
  hello.c

4) When Willow runs her program from the command line, she gets the following error? What is happening and how can she fix it?

$ ls
Makefile  fortune  fortune.c  hello  hello.c
$ hello
Command 'hello' not found

5) The following program crashes. What is the problem and how can we fix it?

#include <stdio.h>

int main() {
  int* value = NULL;
  int a = 4;

  printf("value is %d\n", *value);
}

6) The following program crashes. What is the problem and how can we fix it?

#include <stdio.h>
#include <string.h>

void initialize(char text[]) {
  strcpy(text, "pina collada");
}

int main() {
  char str1[5];
  initialize(str1);
  printf("%s\n", str1);
  return 0;
}

7) What is the output of this program?

#include <stdio.h>

int arg_modifier(int x, int *y);

int main() {
    int val1, val2, ret;

    printf("Enter a value: ");
    scanf("%d", &val1);
    printf("Enter another value: ");
    scanf("%d", &val2);

    // pass val1 by value and val2 by pointer:
    printf("before call: val1 = %d val2 = %d\n", val1, val2);
    ret = arg_modifier(val1, &val2);
    printf("after call:  val1 = %d val2 = %d ret = %d\n", val1, val2, ret);

    return 0;
}

int arg_modifier(int x, int *y) {
    printf("  in arg_modifier:      x = %d *y = %d\n", x, *y);
    *y = *y + x;
    x = x + 5;
    printf("  leaving arg_modifier: x = %d *y = %d\n", x, *y);

    // Draw function stack here
    return x;
}

8) Draw the state of the function stack and heap for the program above in arg_modifier. Assume the user entered the values 6 and 1. Draw the stack at the point in the execution right before the return from the arg_modifier function, and consider the following questions:

Where are variables val1 and val2 located on the stack?
Where are the parameter values located?
What value does each parameter get?
What variables are in scope of arg_modifier?

9) Consider the following code. Find and fix the errors in the associated stack diagram.

float foo(float* vals, int n)
{
  float x = 0.0;
  for (int i = 0; i < n; i++)
  {
    x += vals[i];
  }
  return x;
}

void main()
{
  float heights[3] = {6.1f, 5.2f, 4.9f};
  float a = foo(heights, 3);
  float b = a / 3;
  // draw stack here
  printf("%.2f\n", b);
}

10) Write code that implements a power function (for positive integer exponents only). A call to your function should compute \(base^{exp}\) and might look like:

result = power(base, exp);

11) Write code that implements a function void removeLetter(char* str, char letter) that removes all occurrences of letter from str. Your function should modify the contents of str. (To check your work, implement your program and test it from main).

12) Write code that implements a function isPalindrome that returns 1 if a given string is a palindrome and 0 otherwise. Your function can be iterative or recursive. Test your function from main.