0x05-pointers_arrays_strings

0x05. C - Pointers, arrays and strings

Learning objectives for this project:

• What are pointers and how to use them
• What are arrays and how to use them
• What are the differences between pointers and arrays
• How to use strings and how to manipulate them
• Scope of variables

Tasks 📃

• 0. 98 Battery st.

  • 0-reset_to_98.c: C program that takes a pointer to an int as parameter and updates the value it points to to 98.
    • Prototype: void reset_to_98(int *n);

• 1. Don't swap horses in crossing a stream

  • 1-swap.c: C program that swaps the values of two integers.
    • Prototype: void swap_int(int *a, int *b);

• 2. This report, by its very length, defends itself against the risk of being read

  • 2-strlen.c: C program that returns the length of a string
    • Prototype: int _strlen(char *s);

• 3. I do not fear computers. I fear the lack of them

  • 3-puts.c: C program that prints a string, followed by a new line, to stdout.
    • Prototype: void _puts(char *str);

• 4. I can only go one way. I've not got a reverse gear

  • 4-print_rev.c: C program that prints a string in reverse, followed by anew line.

• 5. A good engineer thinks in reverse and asks himself about the stylistic consequences of the components and systems he proposes

  • 5-rev_string.c: C program that reverses a string.
    • Prototype: void rev_string(char *s);

• 6. Half the lies they tell about me aren't true

  • 6-puts2.c: C program that prints every other character of a string, starting with the first character, followed by a new line.
    • Prototype: void puts2(char *str);

• 7. Winning is only half of it. Having fun is the other half

  • 7-puts_half.c: C program that prints half of a string, followed by a new line.
    • Prototype: void puts_half(char *str);
    • The function should print the second half of the string
    • If the numbers of characters is odd, the function should print the last n characters of the string, where n = (length_of_the_string - 1) / 2

• 8. Arrays are not pointers

  • 8-print_array.c: C program that prints n elements of an array of integers, followed by a new line.
    • Prototype: void print_array(int *a, int n);
    • Where n is the number of elements of the array to be printed
    • Numbers must be separated by comma, followed by a space
    • The numbers should be displayed in the same order as they are stored in te array
    • printf is allowed

• 9. strcpy

  • 9-strcpy.c: C program that copies the string printed by src, including the terminating null byte (\0), to the buffer pointed to by dest
    • Prototype: char *_strcpy(char *dest, char *src);
    • Return value: the pointer to dest

• 10. Great leaders are willing to sacrifice the numbers to save the people. Poor leaders sacrifice the people to save the numbers

  • 100-atoi.c: C program that converts a string to an integer
    • Prototype: int _atoi(char *s);
    • The number in the string can be preceded by an infinite number of characters
    • Need to take into account all the - and + signs before the number
    • If there are no numbers in the string, the function must return 0
    • Not allowed to use long
    • Not allowed to declare new variables of "type" array
    • Not allowed to hard-code special values
    • The gcc flag -fsanitize=signed-integer-overflow will be used to compile the code.

• 11. Don't hate the hacker, hate the code

  • 101-keygen.c: C program that generates random valid passwords for the program 101-crackme.
    • Not allowed to use standard library
    • betty-style test are not compulsory but betty-doc tests are
    • man srand, rand, time
    • gdb and objdump can help