Tutorial 2 (Sep 21): getchar(), putchar(), scanf(), printf(), strcpy(), strlen()

Topics

  • characters, string literals, strings (character arrays)
  • getchar(), putchar()
  • scanf(), printf()
  • strcpy(), strlen()

In-Class Exercises

input/output

strcopy

Characters, string literals, strings (character arrays)

  •  int c = 'A'; // c = 65, since the ASCII value of 'A' is 65
    • a character in C is stored as an integer
    • this integer represents the ASCII value of the character
    • you can freely convert between a character and an int, since it is stored as an int

  • char string_name[100] // create a character array of size 100
    • C has no primary construct for strings
    • a string is represented/stored as an array of characters
    • the char array is manipulable ie. you can change the contents freely
    • however, the size of the array is fixed. To change the size of the memory block containing your array, you can use realloc()

  • char *mystring = "hello, world!"; // create a string literal containing my string
    • a string literal is a pointer to a read-only memory block, containing the string
    • *mystring is the pointer to where mystring is stored (the start of the string literal)
    • *(mystring+1) will return the second character of the string literal (in this case, the letter "e")

getchar(), putchar()

  •  getchar()
    • gets one single character from the user
    • NOTE: when the user types a character then presses ENTER (eg. <a><ENTER>), the letter 'a' is grabbed by getchar(), while the <ENTER> stays in the buffer. If you read from the buffer using getchar() or scanf() after, it will first read the leftover <ENTER>, before reading any other input from the user.

  • putchar(int char)
    • prints one character to the output
    • you can use putchar('\n') to print a newline character

scanf(), printf()

  • scanf(const char *format, ...)
    • gets user input, according to the format specified (eg. %s for a word, %d for text, %[a-ZA-Z] for all letters, %[ a-zA-Z] for all letters plus spaces, %[^\t\n] for anything other than tab/newline characters)
    • eg. scanf("%s", string_to_save_to); // get the first word (delimited by a space), and save it to string_to_save_to
    • eg. scanf("Numbers: %d %d", first_num, second_num); // if the user types Numbers: 10, 20, then first_num = 10 and second_num = 20)
  • printf(const char *format, ...)
    • prints strings to output, along with any variables provided as arguments 
    • eg. printf("%s", string_to_print); // print the first word saved in string_to_print
    • eg. printf("Your two numbers are %d and %d.", first_num, second_num) // if first_num = 10 and second_num = 20, then the output is "Your two numbers are 10 and 20."

strcpy()

  •  strcpy(char *dest, const char *src)
    • copies the string value of the src to dest
    • C does not have a primary construct for strings, so you need to include <string.h> to use strcpy() and other string manipulation methods (eg. strlen() )
    • trying to copy a string like in Java will result in only copying the pointer
    • to copy the value of the string (which the pointer is pointed at), we need to use strcpy()