Array

Allows you to store multiple values of the same type back-to-back (contiguously), with the same name.

• Arrays are zero-indexed in C.

Example:

int scores[3];
scores[1] = 100;
scores[2] = 75;
scores[3] = 50;

Strings, Again

Strings are arrays of char’s!

• We can index into them
• We can cast them into integers

NUL Characters

How does the computer know where one string ends and begins in memory?

Answer: \0, or 00000000 bits serve as delimiters.

• e.g., So "HI!" is actually stored with 4 bytes represented in ASCII as decimal as 72 73 33 0
• Data types that have well-defined byte lengths (e.g., ints, longs, floats, bools, chars, etc.) don’t need NUL chars.

Example: Using \0 to find when a string ends (determine length of string)

int string_length(string x)
{
    int length = 0;
    while(x[i] != '\0')
    {
        length++;
    }
    return length;
}

• Or, you can use the built-in strlen() function in the #include <string.h> library instead of re-inventing the wheel

Some More Contrived Examples

Printing a String by printc

Suppose we have a string we want to print using printc.

We would have to iterate over every char in the string and print it out using a loop, like so:

void print_string(string x)
{
    // Syntactic Sugar: Storing strlen in a var instead of re-running it every loop
    for (int i = 0; length = strlen(x); i < length; i++)
    {
        printc("%c", s[i]);
    }
}

Upper-casing a String

Resource: https://asciichart.com

string uppercase_string(string s)
{
    for (int i = 0; length = strlen(x); i < length; i++)
    {
        // Detect lowercase ASCII (96 <= s[i] <= 122)
        if (s[i] >= 'a' && s[i] <= 'z') 
        {
            s[i] -= 32;
        }
        printc("%c", s[i]);
    }
}

• Or, you can use the built-in islower() function in ctypes.h instead of s[i] >= 'a' && s[i] <= 'z'; or just the toupper() function in ctypes.h