CMSC104

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Lecture 20: Arrays Classwork

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Reading Assigned:   8.1 - 8.3 and 9.1

Homework Due:  Homework 09

Homework Assigned:  Homework 10

Classwork Assigned:  Classwork 11

Topics Covered:

• Quiz 3 Results
• Homework 9 questions?
• Homework 10 overview
• Arrays
  • Reminder of array syntax

    int x[10];
    int i;
    for(i=0; i<10; i++) {
      x[i] = 100 + i;
    }
    for(i=0; i<10; i++) {
      printf("x[%d] is %d\n", i, x[i]);
    }
    

  • Reminder about how arrays are stored in memory
  • Arrays are stored in sequential memory locations
  • You must be sure you don't access array elements outside of the allocated size
  • Use conditionals and loops to ensure index is valid
• Strings
  • An example of a string in C "hello"
  • Strings are just an array of characters
  • We can create a string by saying:

        char c[] = "hello";
    

  • Strings in C always contain one extra character, a character at the end of the string with the value zero called NULL
  • The null character can also be written as '\0'
  • We can print strings via printf with:

        char c[] = "hello";
        printf("%s", c);
    

  • This code will print the output "hello"
  • We can also get string input from the user with scanf:

        char c[20];
        scanf("%19s", &c);
        printf("%s", c);
    

  • Note the value 19 we passed to scanf between % and s, that says that scanf should put at most 19 characters into the string
  • The %s specifier to scanf will read all the characters upto the maximum value specified, or the first whitespace character (space, tab, return)