Strings: Text in C

A string is an array of characters

C has no special text type. A piece of text – a string – is simply an array of chars:

#include <stdio.h>

int main() {
    char name[20] = "Asha";
    printf("Hello, %s!\n", name);
    printf("First letter: %c\n", name[0]);
    return 0;
}

Output

Hello, Asha!
First letter: A

• char name[20] makes room for up to 20 characters.
• %s prints a whole string.
• name[0] is one character, so we print it with %c.

The hidden '\0' at the end

How does printf know where the text stops? C puts a special invisible character at the end of every string: '\0', called the null character. So "Asha" really takes 5 places:

Think of it like this: '\0' is like the full stop at the end of a sentence. It tells everyone reading: "the text ends here".

Remember: A string needs one extra place for '\0'. To store a word of 10 letters, the array needs at least 11 places.

Changing letters

Because a string is an array, you can change single letters:

#include <stdio.h>

int main() {
    char word[10] = "cat";
    word[0] = 'b';
    printf("%s\n", word);
    return 0;
}

Output

bat

Reading a word

scanf with %s reads one word. Notice: no & here! An array name already tells scanf where the memory is.

#include <stdio.h>

int main() {
    char city[30];
    printf("Where do you live? ");
    scanf("%s", city);
    printf("\n%s is a nice place!\n", city);
    return 0;
}

Input (what the user types)

Mumbai

Output

Where do you live? 
Mumbai is a nice place!

Common mistake: scanf("%s", ...) stops at the first space. If the user types New York, you only get New. The last lesson of this module shows how to read a whole line.