This document discusses the key elements of a minimal C program, including the main function header, return statements, standard libraries, variables, input/output functions, and debugging tools. It explains that a basic C program contains an int main function within curly brackets that typically returns 0, and may include standard libraries like stdio.h for input/output. Variables are declared with data types and assigned values through statements. Common errors like syntax issues or logical bugs can be debugged using tools like gdb.

1. Minimal standard C program
int main(void) {
return 0 ;
}

2. Function header
int main(void)
• Return type
– Integer according to ANSI C standard
• Return 0, for success
• Or better yet, return EXIT_SUCCESS
• Return non-zero, otherwise
• Name of function
• Argument types
– void means no arguments
– More later on (int argc, char *argv[])

3. C block
• Delimited by “curlies” – { }
– Encloses C statements (more later)
– Starts with variable declarations (more later)
• C90 and C++ are more forgiving
– Can be nested
• Function code must be in a block

4. Minimal C program with I/O
#include <stdio.h>
int main(void) {
printf("Hello Worldn") ;
return 0 ;
}

5. Standard libraries
• C has many “standard” libraries
– But they really aren’t part of the “language”
• C preprocessor (cpp)
– Processes lines starting with #
• And some other things
• #include <stdio.h>
– Adds ~900 lines of code needed to use standard I/O
– cpp -E prog.c
• Shows what is added

6. Printing a line
• printf("3 feet is 36 inchesn") ;
– Writes a line to standard output
• 3 built-in FILE’s of C
– Standard output (stdout)
• Normal terminal output
– Standard error (stderr)
• Terminal output for errors
– Standard input (stdin)
• Terminal input

7. Escape sequences
Allows inclusion of special characters
n New line
t Horizontal tab
r Line feed
' Single quote
" Double quote
Backslash
And a few more….

8. Formatted I/O
• Allows the pretty printing of variable data
– Easy to get started
– But it takes time to master
• Inspired by FORTRAN I/O
– So it enables printing of aligned tables
• printf("Easy as %8.4fn", PI) ;
– Easy as ____3.1416

9. Variables
• Names and places for data
• Global variables
– Declared outside of blocks
• Local variables
– Declared at beginning of blocks
• In K&R and ANSI C
– Stored on the stack

10. Variable names
• Can contain
– Letters (upper and lower)
– Digits
– Underscore
• Cannot start with a digit
• Cannot be a keyword
– Like return

11. Variable declarations
• Type in C
– Integer, floating point, character, …
– Determines space needed for variable
– Determines what kind of add to do
• Integer or IEEE floating?
• Declaration statements
– int lengthInFeet ;
– int x, y, Y, z ;

12. Assignment statements
• Gives a value to a variable
– variable = expression ;
• For our example
int feet, inches ;
feet = 10 ;
inches = 12*feet ;

13. The whole program
#include <stdio.h>
int main(void) {
int feet, inches ;
feet = 5 ;
inches = 12*feet ;
printf("% d feet is %d inchesn",
feet, inches) ;
return 0 ;
}

14. Things that go wrong
• Syntactic error
– Your program isn’t in legal C
• inches = 12 feet ;
• Semantic error
– Your program has a bug
• inches = feet/12 ;

15. Debuggers
• Programs to “step” through your code
• Linux gcc has gdb
– Must compile with debugging symbols
• gcc -g ……..
– Many features
• Set breakpoint
• Examine variables
– Hard to master
• But worth the effort to learn a little

16. Phases
• Compiling
– Preprocessor
• Expands #include statements
– Lexical analysis
• Finds the tokens (or words)
– Syntactic analysis
• Finds the expressions, statements, blocks, etc.
– Code generation
• Linking
– Adds in the library routines
• Loading
– Processes DLL’s and relocation (if needed)