Strings

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• Week 4 Wednesday 25/06/2025 12PM-2PM - Bongo/Tabla Lab (K17 G07/G08)

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Assignment 1

• Releasing really soon
• Watch the Assignment Walkthrough video
• Submission in ~Week 7
• Worth 20%

Arrays recap

• A collection of data, all of the same type. (homogeneous)
• We have a single identifier for the entire array
• It is a random access data structure, meaning we can access any element in the array at any time

Declare + initialise

int ice_cream_per_day[7] = {3, 2, 1, 2, 1, 3, 5};

^ Note you can only do this when you declare, not later!

int ice_cream_per_day[7] = {};

^ Will initialise all elements to 0

Some corrections

int my_data[] = {3, 2, 1, 2, 1, 3, 5};

^ Will create a 7-element array

int my_data[14] = {3, 2, 1, 2, 1, 3, 5};

^ Will create a 14-element array, with the first 7 elements then 7 0'd out

Strings!

• Strings are multi-character words
• "Jake Renzella" -> is a string with 13 characters!
• Strings are great! They are everywhere!

Strings in C are char arrays

• A collection of characters
• C does know how to work with char[]s

#include <stdio.h>

int main(void) {
    char name[3] = {'G', 'a', 'b'};
    // change name to Jake
    // :( can't, won't fit
    
    return 0;
}

#include <stdio.h>
#define MAX_STR 50

int main(void) {
    char name[MAX_STR] = {'J', 'a', 'k', 'e'};

    return 0;
}

The null terminator

• Remember in C, we don't know when arrays end
• We have to keep track of the length ourselves
• We can't always do this with char[]...
• Instead, we place a special character called the null terminator at the end of our character arrays \0

How to use strings in C

• Because strings are character arrays, the type is char[]
• There are two ways to declare a string, here's one:

char word[] = {'h', 'e', 'l', 'l', 'o', '\0'};

Strings are very common

So there are easier ways to use them:

char word[] = "hello";

• This is exactly the same as the previous example
• It includes the null terminator!

String literals

"Jake!"

• uses double quotes " to wrap the string literal
• single quote for characters!

• Used to assign strings to char[] easily:

  char name[] = "Jake Renzella";

Using strings

• printing: printf or fputs
• scanning: fgets
• Both included in <stdio.h>

fgets usage

// Declare the array which will contain the string. Note, we don't know how big the string will be, so let's come up with a maximum.
char my_string[MAX_LENGTH]

// read the string in
fgets(my_string, MAX_LENGTH, stdin);

Reading strings in a loop

• We can read until CTRL+D is entered in the terminal by calling fgets in a loop
• fgets() stops reading when either length-1 characters are read, newline character is read or an end of file is reached, whichever comes first

Printing strings

fputs(array[], stream)

• array[] -> the character array to be printed
• stream -> the location to print, always use stdout in COMP1511

Printing strings

char name[] = "Jake";
fputs(name, stdout);

^ Why doesn't fputs need the LENGTH, like fget?