Intro

A repo for programming exercise.

Log

• 2024/03/09
  • Start c programming exercise based on Learn C The Hard Way (Chiniese Version) .
  • c/ex1: Compile an example for printing "hello world".
  • c/ex2: Simple example of make and Makefile
  • c/ex3: Print with format, and try to make it error/crash, through methods like: not initializing varialbes, not specifying variables in the print command.
• 2024/03/10
  • c/ex4: Install valgrind and use it for printing errors of exeutable.
    • Use curl -O <link> download the compressed .tar.bz2 file. Failed to uncompress with tar xvzf <file> at first with message bzip2: (stdin) is not a bzip2 file.... Root cause is found to be file is broken during downloading, which could be checked by md5sum comparison with that in the download page. Re-downloaded and then fixed.
    • How to change shell of make: By default, make use the POSIX shell (/bin/sh), need to add SHELL := /bin/bash on the top of Makefile to let it use bash. (Ref.)
    • How to pass args to make: (Ref.)
      • Makefile:

        run:
            @echo $(ARGS)
        

        run: make run ARGS="Hello", output: Hello
  • c/ex5: Read a simple c script line by line to know the basic code structure.
  • c/ex6: A script containning multiple variables of different data types. Print them with printf.
  • c/ex7: A simple code for knowing different types of data.
    • 'long' type integer:
      • printf with %ld
      • limit: -2^63 ~ +2^63 - 1
    • printf special char '\0' (null_byte) with:
      • %c -> (empty)
      • %s -> (null)
      • %d -> 0
    • printf char of number zero '0' with %s -> Segmentation fault
    • 'unsigned long' type integer:
      • printf with %lu
      • limit: 0 ~ +2^64 - 1
• 2024/03/23
  • c/ex8: Play with array of numbers, array of chars and string by printf / sizeof
    • string is array of chars ending with null character, i.e. '\0'.
    • sizeof() returns the allocated memory for the operand, so, for a string, it will take the ending null into count, then usually looks 1 more than the number of characters of the string. (Ref.)
  • c/ex9: Involve something like array initialization, assigning string with pointer ... (Not really know what the author wants readers to know....just go through 😅:)
  • c/ex10: Array of strings and loop
    • argv[0] is the command/executable itself.
    • Format of a for loop:

      for(INITIALIZER; TEST; INCREMENTER) {
          CODE;
      }
      

      Executing order: INITIALIZER, TEST, CODE, INCREMENTER, TEST, CODE, INCREMENTER, ... until TEST being false.
• 2024/03/24
  • c/ex11: While loop
    • Format of a while loop:

      while (TEST) {
          CODE;
      }
      

    • Usually for loop is more robust, since it has INITIALIZER and INCREMENTER that help avoiding errors.
    • Way to print the memory address of a variable:

      int var = 0;
      printf("Mem addr of var: %p \n" &var);
      

      output example: Mem addr of var: 0x7ffe2333ce7c
    • 1 byte = 8 bit
      • int -> 4 byte : 2^32 counts , -2^31 ~ +2^31 -1
      • char *[] -> 8 byte : 63 chars + 1 null
  • c/ex12: if - else conditional statement.
    • Better do not omit the curly braces {} for conditional statements.
  • c/ex13: switch statement
    • Compiler will convert it into a jumping table.
    • Don't forget break and default