Strings

In C, strings are arrays of characters. Less convenient than a built-in type, but you'll understand exactly how text works in memory

#include <stdio.h>

int main(void) {
    char name[] = "Ken Thompson";
    printf("%s\n", name);
    return 0;
}

Prints Ken Thompson. The format specifier for a string is %s

What does char name[] = "Ken Thompson" mean? It creates an array of chars containing the letters of the text. char[] is "array of characters", and "" is the way to write a string literal that fills the array

Behind the scenes, every C string ends with a special hidden character: \0 (called the null terminator). It marks the end of the string. So "Tommy" in memory is really T, o, m, m, y, \0: six characters. Functions like printf keep reading until they hit \0

You don't usually write \0 yourself when using string literals. C adds it for you. Just be aware it exists, because forgetting it is a classic source of bugs in C

How long is a string? C has no methods on strings, so we use a function from the standard library

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

int main(void) {
    char name[] = "Ken Thompson";
    printf("%zu\n", strlen(name));   // 12
    return 0;
}

Two new things

#include <string.h>: needed for strlen and friends
%zu: format specifier for the type strlen returns (a size_t, kind of an unsigned int). For our purposes, you can also use %d with a cast: printf("%d\n", (int) strlen(name))

strlen counts up to \0, without including it. So strlen("Ken") is 3, even though the array has 4 spots in memory

Comparing strings, and the biggest C trap around strings

#include <stdio.h>

int main(void) {
    char a[] = "hello";
    char b[] = "hello";

    if (a == b) {   // WRONG
        printf("equal\n");
    }
    return 0;
}

This compares memory addresses, not the contents. a and b are two different arrays in memory, so this never prints equal, even though both contain "hello"

The correct way is strcmp (string compare) from <string.h>

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

int main(void) {
    char a[] = "hello";
    char b[] = "hello";
    if (strcmp(a, b) == 0) {
        printf("equal\n");
    }
    return 0;
}

strcmp returns 0 when the strings are equal. (Yes, equal = 0. C is full of little quirks like that)

A single character at a position. Since a string is just an array, we use indexing

#include <stdio.h>

int main(void) {
    char name[] = "Ken Thompson";
    printf("%c\n", name[0]);    // K
    printf("%c\n", name[4]);    // T
    return 0;
}

%c is the format specifier for a single char. Counting starts from 0, as always

Modifying characters

#include <stdio.h>

int main(void) {
    char name[] = "ken";
    name[0] = 'K';
    printf("%s\n", name);   // Ken
    return 0;
}

We can change individual characters because name is an array we own. Notice the single quotes for a single char ('K'), and double quotes for a string ("Ken"). Confusing them is one of the most common mistakes in C

Mission: Decode the Call Sign

A garbled transmission just came through on the line. The switchboard operator stored it in a char array. Your job: print the full call sign, its length, the first character, and the last character, so the operator can verify the signal.

Read a line of text (it may contain spaces) with fgets into a name[64] array, then strip the trailing newline with strcspn

Print the full name string
Print its length (use strlen)
Print the first character (index 0, use %c)
Print the last character (index strlen(name) - 1, use %c)

Example

Input

dennis ritchie

Output

dennis ritchie
14
d
e

Example

Input

ken thompson

Output

ken thompson
12
k
n