0x05-pointers_arrays_strings

Pointers, Arrays, Strings

• 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

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0. 98 Battery st.

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);

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1. Don't swap horses in crossing a stream

Write a function that swaps the values of two integers

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

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

Write a function that returns the length of a string.

• Prototype: int _strlen(char *s);

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

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

• Prototype: void _puts(char *str);

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

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

• Prototype: void print_rev(char *s);

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

Write a function that reverse a string.

• Prototype: void rev_string(char *s);

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

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);

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

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

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8. Arrays are not pointers

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

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9. strcpy

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

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

Write a function 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
• 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
• Your code would be compiled using the -fsanitize=signed-integer-overflow gcc flag

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

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

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