Chartacter, C-strings(10.1-10.5)

• <cctype>

• Header file you must include to use the character-testing functions (isalpha, isdigit, etc.).

• Return value of character-testing functions

• Technically an int. Nonzero means true, 0 means false.

• isalpha / isdigit / isalnum

• isalpha is true for a letter. isdigit is true for 0 to 9. isalnum is true for a letter or a digit.

• islower / isupper

• islower is true for a lowercase letter. isupper is true for an uppercase letter.

• isspace

• True for whitespace: space, newline (\n), tab (\t), vertical tab (\v).

• 
  

• ispunct vs isprint

  
  

• ispunct is true for a printable character that is NOT a letter, digit, or space. isprint is true for any printable character, including space.

• Loop condition count < size - 1

• Stops before the last array element, which holds the null terminator '\0'.

C-string

Characters stored in consecutive memory and ended by a null terminator '\0'.

Null terminator

'\0', the byte with ASCII code 0. It marks the end of a C-string.

String literal storage

Every string literal is stored as a C-string with '\0' added. "Bailey" uses 7 bytes.

C-string array size

Characters needed plus 1 for '\0'. char name[21] holds at most 20 characters.

char name[] = "Jasmine";

Creates an array with exactly 8 elements: 7 letters plus '\0'.

cin >> name (C-string)

Reads one word and stops at whitespace. No size limit, so it can overflow the array.

cin.getline(line, SIZE)

Reads a whole line, including spaces. Reads at most SIZE - 1 characters, then adds '\0'.

Loop through a C-string

while (s[i] != '\0'). Stop at the null terminator, not at the array size.

Why learn C-strings

Legacy C++ code, library functions that need them, and C libraries all use C-strings.

toupper(ch)

Returns the uppercase equivalent of ch. Non-letters and uppercase letters are returned unchanged.

tolower(ch)

Returns the lowercase equivalent of ch. Non-letters and lowercase letters are returned unchanged.

Does toupper change its argument?

No. It only returns the converted value. You must store the result to keep it.

Case-insensitive input check

Convert with toupper or tolower, then compare once. Example: toupper(goAgain) != 'Y'.

atoi / atol / atof

Convert a C-string to int, long, or double. Need . Bad input is undefined.

stoi / stol / stod (and similar)

Convert a string or C-string to int, long, or double. Need .

stoi with invalid or too large input

Invalid input throws invalid_argument. A value out of range throws out_of_range.

to_string(value)

Converts a number to a string object. Needs .

Newline problem

cin >> leaves the newline in the buffer, so the next getline reads an empty line.

Two fixes for the newline problem

Call cin.ignore() before getline, or read all input with getline and convert with stoi or stod.

Average with integers

Use static_cast(total) / count to avoid integer division.

Header for C-string functions

#include

strlen(s)

Returns the number of characters before the null terminator. Not the array size.

strcat(s1, s2)

Appends s2 to the end of s1. s1 changes, s2 does not. Adds no space. s1 must be big enough.

strcpy(dest, src)

Copies src into dest, including the null terminator. Overwrites dest. No bounds checking.

strncat(s1, s2, n)

Like strcat but appends at most n characters from s2. Safer.

strncpy(s1, s2, n)

Like strcpy but copies at most n characters. If n is not greater than the length of s2, no null terminator is added, so add it yourself.

strstr(s1, s2)

Returns the address of the first s2 inside s1, or nullptr if not found.

strcmp(s1, s2)

Returns 0 if equal, negative if s1 comes before s2, positive if s1 comes after s2. Case sensitive.

Why not use == to compare C-strings?

C-strings are arrays. == compares addresses, not characters. Use strcmp.

!strcmp(a, b)

True when the two strings are equal.