Study Guide 1

Code Jams are open book. 40 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) 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

4) Implement and test 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);

5) Implement a function void removeLetter(char* str, char letter) that removes all occurrences of letter from str. Your function should modify the contents of str. Test your function from main.

6) Implement 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.

7) 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);
}

8) 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;
}

9) 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;
}

10) 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?