UMBC CMSC201, Computer Science I, Fall 1994 Sections 0101, 0102 and Honors

Tuesday September 13, 1994

Assigned Reading: 2.1

Handouts (available on-line): none

Topics Covered:

• Simplified computer architecture and why we don't program in machine language and assembly language any more.

• A simple C program that prints out "Hello World" and sample run. Note the #include preprocessor directives.

• Embellishments: hello2.c and sample run. Note the use of \n, \\ and %%.

• A program to add two integers: add2.c and sample run. See how integer variables are declared and used. Note the use of %d in the printf function. In the sample run, see that GetInteger() is robust and will not allow the user to enter a number that is not an integer.

• A program to add two floating point numbers: add2f.c and sample run. Floating point numbers are declared using double and printed using %g. Double variables are read in using GetReal(). Round off errors may occur (as with hand-held calculators).

• A program that reads in a string and prints it out: greeting.c and sample run. String variables are declared using string and read in using GetLine().

• Some typical coding errors and how the compiler might respond to them:
  • In this program, wrong1.c, the functions GetInteger and printf() are misspelled. The sample run also shows what happens if you didn't copy cc201 correctly.
  • In this program, wrong2.c, the preprocessor directive #include is misspelled. There is also a missing end quote in the printf() statement on line 19. The sample run also shows the error messages generated in these situations.
  • In this program, wrong3.c, a semicolon is missing at the end of the variable declarations on line 14. The sample run shows that the compiler complains about a syntax error on line 16. This is because C ignores whitespace (spaces, newlines and tabs) and does not notice the missing semicolon until it sees the printf(). The corrected program correct3.c, shows that we can put the declaration of total in a completely weird place and the complier does not care, as witnessed by the sample run.