Arrays and Strings

Character Arrays

C strings are arrays of characters ending with a null terminator.

null terminator The `'\0'` character marks where a C string ends.
mutable characters Changing one array element changes the visible string content.

Character Arrays

first
char_arrays.c
Replay: real traced execution (multi-file project)
#include <stdio.h>

int main(void) {
    char word[4] = {'c', 'a', 't', '\0'};
    char first = 'C';

    word[0] = first;

    printf("word=%s\n", word);
    return 0;
}

#include <stdio.h>

int main(void) {
    char word[4] = {'c', 'a', 't', '\0'};
    char first = 'B';

    word[0] = first;

    printf("word=%s\n", word);
    return 0;
}

#include <stdio.h>

int main(void) {
    char word[4] = {'c', 'a', 't', '\0'};
    char first = 'R';

    word[0] = first;

    printf("word=%s\n", word);
    return 0;
}

  1. word ← cat, first ← C, word[0] ← C

    3int main(void) {4    char word→ cat[4] = {'c', 'a', 't', '\0'};5    char first→ C = 'C'; //@first='B', 'R'67    word[0]→ C = firstC;89    printf("word=%s\n", wordCat);10    return 0;11}
    outputword=Cat

  1. word ← cat, first ← B, word[0] ← B

    3int main(void) {4    char word→ cat[4] = {'c', 'a', 't', '\0'};5    char first→ B = 'B';67    word[0]→ B = firstB;89    printf("word=%s\n", wordBat);10    return 0;11}
    outputword=Bat

  1. word ← cat, first ← R, word[0] ← R

    3int main(void) {4    char word→ cat[4] = {'c', 'a', 't', '\0'};5    char first→ R = 'R';67    word[0]→ R = firstR;89    printf("word=%s\n", wordRat);10    return 0;11}
    outputword=Rat