string.h

The string toolbox

#include <string.h> gives you: strlen(s) the length (without the '\0'), strcpy(dst, src) copy, strcat(dst, src) append, and strcmp(a, b), which is 0 when equal, negative when a comes first in dictionary order, positive otherwise.

a == b on two strings compares their addresses, not their letters. Always use strcmp.

strcpy and strcat don't check sizes: the destination must be big enough, or they write past its end.

Length and comparison

#include <stdio.h>
#include <string.h>

int main() {
    char a[20] = "pen";
    char b[20] = "pencil";
    strcat(a, "s");
    printf("%d %d\n", (int) strlen(a), strcmp(a, "pens") == 0);
    printf("%d\n", strcmp(a, b) > 0);
    return 0;
}

What does this print?

• 4 1 1
• 3 0 0
• 4 1 0

Exercise: Password check

This should print Welcome when the typed word is open123, otherwise Denied. It always says Denied. Fix the comparison.

Exercise: Longest word

Read n (1 to 50), then n words (each under 30 letters). Print the longest word; if there's a tie, the one that came first.