0x05-pointers_arrays_strings

0x05. C - Pointers, arrays and strings

Learning Objectives

At the end of this project, you are expected to be able to explain to anyone, without the help of Google:

General

• 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-reset_to_98.c

Write a function 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-swap.c

Write a function that swaps the values of two integers.

• Prototype: void swap_int(int *a, int *b);

2-strlen.c

Write a function that returns the length of a string.

• Prototype: int _strlen(char *s); FYI: The standard library provides a similar function: strlen. Run man strlen to learn more.

3-puts.c

Write a function that prints a string, followed by a new line, to stdout.

• Prototype: void _puts(char *str); FYI: The standard library provides a similar function: puts. Run man puts to learn more.

4-print_rev.c

Write a function that prints a string, in reverse, followed by a new line.

• Prototype: void print_rev(char *s);

5-rev_string.c

Write a function that reverses a string.

• Prototype: void rev_string(char *s);

6-puts2.c

Write a function that prints every other character of a string, starting with the first character, followed by a new line.

• Prototype: void puts2(char *str);

7-puts_half.c

Write a function 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 number of characters is odd, the function should print the last n characters of the string, where n = (length_of_the_string - 1) / 2

8-print_array.c

Write a function 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 the array
• You are allowed to use printf

9-strcpy.c

Write a function that copies the string pointed to 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 FYI: The standard library provides a similar function: strcpy. Run man strcpy to learn more.

100-atoi.c

Write a function that convert a string to an integer.

• Prototype: int _atoi(char *s);
• The number in the string can be preceded by an infinite number of characters
• You 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
• You are not allowed to use long
• You are not allowed to declare new variables of “type” array
• You are not allowed to hard-code special values
• We will use the -fsanitize=signed-integer-overflow gcc flag to compile your code. FYI: The standard library provides a similar function: atoi. Run man atoi to learn more.

101-keygen.c

Create a program that generates random valid passwords for the program 101-crackme.

• You are allowed to use the standard library
• You don’t have to pass the betty-style tests (you still need to pass the betty-doc tests)
• man srand, rand, time
• gdb and objdump can help