Laboratory: Strings in C

Summary: In this laboratory, you will experiment with C's strings and the various standard string procedures.

Contents:

• Preparation
• Exercises
  • Exercise 1: Printing Strings
  • Exercise 2: Declaring Strings
  • Exercise 3: Uninitialized Strings
  • Exercise 4: Assigning Strings
  • Exercise 5: Concatenating Strings
  • Exercise 6: Reversing Strings
  • Exercise 7: Reversing Strings, Revisited
  • Exercise 8: Reversing Strings, Re-Revisited
  • For Those with Extra Time
    • Extra 1: The Name Game

Preparation

Create a new directory for this laboratory. I'd suggest calling it Labs/Strings.

Exercises

Exercise 1: Printing Strings

Consider the following two mechanisms for printing the string antelope.

a. Which do you prefer? Why?

• printf(antelope);
• printf("%s", antelope);

b. Write a simple program in which the two statements have different output.

Exercise 2: Declaring Strings

Here are a number of different string declarations.

  char *baboon;
  char *chimpanzee = "animal";
  char dolphin[];
  char emu[] = "animal";
  char fox[8];
  char fox[8] = "animal";

a. Which are valid and which are invalid?

b. How do the valid declarations differ?

Exercise 3: Uninitialized Strings

a. Consider the following declaration and code

  char gorilla[8];
  char ch;
  ...
  printf("sizeof(gorilla): %d\n", sizeof(gorilla));
  printf("strlen(gorilla): %d\n", strlen(gorilla));
  printf("gorilla: '%s'\n", gorilla);

What do you expecct the output to be?

b. How would your answer change if gorilla were declared with

  char *gorilla;

c. Verify your hypotheses experimentally.

d. What do your results suggest?

Exercise 4: Assigning Strings

Suppose hippo and iguana are both declared as strings. When, if ever, is

  iguana = hippo;

a valid assignment?

Note that you may need to try different kinds of declarations. (E.g., both could be declared as arrays of characters, both could be declared as pointers to characters, or each could be declared differently.)

Exercise 5: Concatenating Strings

Consider the folling declarations:

  char jackal[8] = "animal";
  char koala[8] = "animal";
  char lemur[8] = "animal";

a. What do you expect the effect of the following instruction to be?

  strcat (koala,"istic");

You may find it useful to read the man page for strcat.

b. Verify your answer experimentally. Make sure to print out all three strings.

c. Explain your answer.

d. Assume you didn't execute the instruction from step a. What do you expect the effect of the following instruction to be?

  strcat (koala, "ed");

e. Verify your answer experimentally. Make sure to print out all three strings.

f. Explain your answer.

Exercise 6: Reversing Strings

Write a procedure, char *reverse (char *str), that reverses the order of characters in str and returns the modified str. Your procedure should modify str.

Exercise 7: Reversing Strings, Revisited

a. Change the parameter to reverse to read const char *str.

b. What effect do you expect this change to have?

c. Check your answer experimentally.

d. Remove the const declaration.

Exercise 8: Reversing Strings, Re-Revisited

Why do you think I did not have you write reverse so that it returns a new string?

Discuss your answer with your neighbor. Be prepared to discuss it with the class.

For Those with Extra Time

Extra 1: The Name Game

Write a program that implements the Name Game.