Lesson 9: Strings
This lesson is one on strings. Strings are really
arrays, but there are some different
functions that are used for strings, like adding to
strings, finding the length of strings, and
also of checking to see if strings match. Strings are
basically sentences, or words. Like,
"This is a string".
Strings are basically character arrays. For example, to
declare a string of 50 letters, you
would want to say:
char string[50];
This would declare a string with a length of 50
characters. Don't forget that arrays begin at
0, not 1 for the index-number. Also, a string ends with
a null character, literally a '/0'
character. But, just remember that there will be an
extra character on the end on a string. It
is like a period at the end of a sentence, it is not
counted as a letter, but it still takes up
a space.
What are strings useful for? Well, for one thing, you
might want to get a person's name. If you
wanted to, you would need a string, because a name can't
fit in one variable! It is, however, a
collection of characters, and so fits nicely into a
character array.
Now, what if you want to input a string? Well, if you
try to use cin>> then it won't work! It
terminates at the first space. However, you can use the
function gets(char *s);
.
Gets is basically a function that reads in a string and
stops reading at the first new-line, for
example, when a user hits enter. Gets is in
stdio.h.
All you do, is put the name of the array and it will
work out,
because the pointer char *s is basically one way you
tell a function that you will be passing an
array, although it is a pointer, it is still the string
you give. Essentially, char *s points to
a string, and you can access this string just like an
array.
I will touch upon this relationship as described above
in another lesson that will be a more
advanced lesson on pointers and arrays.
Anyway, to get a string from a user you want to use
gets. An example program of this would be:
#include <stdio.h> //For
gets
#include <iostream.h> //For all other input/output
functions
void main()
{
char astring[50]; //This declares a character array that
can be used as a string
cout<<"Please enter a string"; //You should know this
one!
gets(astring); //The user will input a string(with
spaces)
cout<<"You input: "<<endl; //You know this one too!
cout<<astring; //This is how you output character
arrays, but not others!
}
Ok, thats pretty simple. But, what if you want to use
some of the nifty functions from string.h?
Well, these include the following functions:
int strcmp(const char *s1,
const char *s2);
strcmp will accept two strings. It will return an
integer. This integer will either be:
Negative if s1 is less than s2.
Zero if s1 and s2 are equal.
Positive if s1 is greater than s2.
Strcmp is case sensitive.
int strcmpi(const char *s1,
const char *s2);
strcmp will accept two strings. It will return an
integer. This integer will either be:
Negative if s1 is less than s2.
Zero if the s1 and s2 are equal.
Positive if s1 is greater than s2.
Strcmpi is not case sensitive, if the words are
capitalized it doesn't matter.
char *strcat(char *desc,
char *src);
strcat is short for string cacatenate, which means to
add to the end, or append. It does just this,
the first string is what the second string is stuck on
the end of. It basically returns the
cacatenated string. The first string will also have the
entire string added to it.
char *strupr(char *s);
strupr converts a string to uppercase. It also returns a
string, which will all be in uppercase.
The input string, if it is an array, will also all be
uppercase.
char *strlwr(char *s);
strlwr converts a string to lowercase. It also returns a
string, which will all be in uppercase.
The input string, if it is an array, will also all be
uppercase.
size_t strlen(const char
*s);
strlen will return the length of a string, minus the
termating character(/0). The size_t is
nothing to worry about. Just treat it as an integer.
Some of the stuff in the strings may be confusing. The
const char *s stuff, for example. But,
just remember that basically all of that will be a
string! It doesn't matter what the code is
right now, just what the functions do.
Now, a small program using many of the string functions!
#include <iostream.h> //For
cout
#include <string.h> //For many of the string functions
#include <stdio.h> //For gets
void main()
{
char name[50]; //Declare variables
char lastname[50]; //This could have been declared on
the last line...
cout<<"Please enter your name: "; //Tell the user what
to do
gets(name); //Use gets to input strings with spaces or
just to get strings after the user presses enter
if(!strcmpi("Alexander", name)) //The ! means not,
strcmpi returns 0 for equal strings
{ //strcmpi is not case sensitive
cout<<"That's my name too."<<endl; //Tell the user if
its my name
}
else //else is used to keep it from always outputting
cout<<"That's not my name."
{
cout<<"That's not my name."<<endl;
}
cout<<"What is your name in uppercase..."<<endl;
strupr(name); //strupr converts the string to uppercase
cout<<name<<endl;
cout<<"And, your name in lowercase..."<<endl;
strlwr(name); //strlwr converts the string to lowercase
cout<<name<<endl;
cout<<"Your name is "<<strlen(name)<<" letters long"<<endl;
//strlen returns the length of the string
cout<<"Enter your last name:";
gets(lastname); //lastname is also a string
strcat(name, " "); //We want to space the two names
apart
strcat(name, lastname); //Now we put them together,we a
space in the middle
cout<<"Your full name is "<<name; //Outputting it all...
}
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