1. Character
A character
is a single alphabet, digit, or symbol enclosed in single quotes (' ').
char ch = 'A';
Example:
char grade = 'B';
char digit = '9';
char symbol = '#';
Memory:
Each
character uses 1 byte in memory.
Character Handling Functions in C
All these functions are declared in the <ctype.h> header file.
They are used to check or convert characters.
isalpha(ch)
Use: Checks whether the character is an alphabet (A–Z or a–z).
Returns:
Example:
Output:
isdigit(ch)
Use: Checks whether the character is a digit (0–9).
Example:
Output:
isalnum(ch)
Use: Checks whether the character is alphanumeric (either a letter or a digit).
Example:
Output:
isspace(ch)
Use: Checks if the character is a space, tab, or newline character.
Example:
Output:
isupper(ch)
Use: Checks whether the character is uppercase (A–Z).
Example:
Output:
islower(ch)
Use: Checks whether the character is lowercase (a–z).
Example:
Output:
toupper(ch)
Use: Converts a lowercase character to uppercase.
Example:
Output:
tolower(ch)
Use: Converts an uppercase character to lowercase.
Example:
Output:
2. Character
Functions (from <ctype.h>)
|
Function
|
Meaning
|
Example
|
Result
|
|
isalpha(ch)
|
Checks if
ch is an alphabet
|
isalpha('A')
|
True
|
|
isdigit(ch)
|
Checks if
ch is a digit
|
isdigit('5')
|
True
|
|
isalnum(ch)
|
Checks if
ch is alphabet or digit
|
isalnum('A')
|
True
|
|
isspace(ch)
|
Checks if
ch is space/tab
|
isspace(' ')
|
True
|
|
isupper(ch)
|
Checks if
ch is uppercase
|
isupper('M')
|
True
|
|
islower(ch)
|
Checks if
ch is lowercase
|
islower('a')
|
True
|
|
toupper(ch)
|
Converts
to uppercase
|
toupper('b')
|
'B'
|
|
tolower(ch)
|
Converts
to lowercase
|
tolower('G')
|
'g'
|
3. Character
Array (String)
Definition:
A character
array is a collection of characters stored in continuous memory.
When it ends with \0 (null character), it becomes a string.
char name[10] = "Ravi";
Internally
stored as:
{'R', 'a', 'v', 'i', '\0'}
Declaration:
char name[20]; // only declared
char city[20] = "Balrampur"; // declared and initialized
4. Input / Output
Functions for Strings
|
Function
|
Description
|
Example
|
|
scanf("%s", str);
|
Takes
input (stops at space)
|
HelloWorld
|
|
fgets(str, size, stdin);
|
Takes
input with spaces (safe)
|
"Hello World"
|
|
printf("%s", str);
|
Prints
string
|
|
|
puts(str);
|
Prints
string with newline
|
|
Example:
#include <stdio.h>
int main() {
char name[30];
printf("Enter
your name: ");
fgets(name, sizeof(name),
stdin);
printf("Hello
%s", name);
return 0;
}
5. String
Functions (from <string.h>)
|
Function
|
Meaning
|
Example
|
Output
|
|
strlen(str)
|
Finds
length of string
|
strlen("Hello")
|
5
|
|
strcpy(dest, src)
|
Copies one
string to another
|
strcpy(a, b)
|
a = b
|
|
strcat(dest, src)
|
Joins two
strings
|
"Good" +
"Morning"
|
"GoodMorning"
|
|
strcmp(str1, str2)
|
Compares
two strings
|
"abc", "abc"
|
0 (equal)
|
|
strrev(str)
|
Reverses
string (non-standard)
|
"abc"
|
"cba"
|
|
strupr(str)
|
Converts
to uppercase (non-standard)
|
"hi"
|
"HI"
|
|
strlwr(str)
|
Converts
to lowercase (non-standard)
|
"HI"
|
"hi"
|
Example:
#include <stdio.h>
#include <string.h>
int main() {
char s1[20]
= "Hello";
char s2[20]
= "World";
printf("Length:
%lu\n", strlen(s1));
strcat(s1,
s2);
printf("Concat:
%s\n", s1);
strcpy(s2, "C
Language");
printf("Copy:
%s\n", s2);
printf("Compare:
%d\n", strcmp("abc", "abd"));
return 0;
}
Output:
Length: 5
Concat: HelloWorld
Copy: C Language
Compare: -1
String Manipulation Functions
in C
1) String Manipulation Functions are predefined functions in C language (available in
the header file <string.h>) that are used to perform various operations on strings,
such as:
finding length, copying, joining, comparing, changing case, or reversing
strings.
1. strlen() – String Length
Syntax:
int strlen(string);
Use:
Finds the total number of characters in a string (excluding '\0').
Example:
char name[] = "India";
printf("%d", strlen(name)); // Output: 5
2. strcpy() –
Copy String
Syntax:
strcpy(destination, source);
Use:
Copies one string into another.
Example:
char str1[20] = "Hello";
char str2[20];
strcpy(str2, str1);
printf("%s", str2); // Output: Hello
3. strcat() – Concatenate (Join) Strings
Syntax:
strcat(string1, string2);
Use:
Joins string2 at the end of string1.
Example:
char s1[20] = "Good ";
char s2[20] = "Morning";
strcat(s1, s2);
printf("%s", s1); // Output: Good Morning
4. strcmp() – Compare Two Strings
Syntax:
strcmp(string1, string2);
Use:
Compares two strings:
- Returns 0 if both are
equal
- Returns positive if
string1 > string2
- Returns negative if
string1 < string2
Example:
char a[] = "apple";
char b[] = "apple";
if(strcmp(a, b) == 0)
printf("Both
strings are same");
else
printf("Different
strings");
5. strrev() – Reverse String
Syntax:
strrev(string);
Use:
Reverses the given string.
Example:
char word[10] = "C";
strrev(word);
printf("%s", word);
6. strupr() – Convert to Uppercase
Syntax:
strupr(string);
Use:
Converts all characters to uppercase.
Example:
char name[20] = "india";
strupr(name);
printf("%s", name); // Output: INDIA
7. strlwr() – Convert to Lowercase
Syntax:
strlwr(string);
Use:
Converts all characters to lowercase.
Example:
char city[20] = "DELHI";
strlwr(city);
printf("%s", city); // Output: delhi
Complete Program Example
Program showing use of all string
manipulation functions.
#include <stdio.h>
#include <string.h>
int main() {
char str1[50]
= "Hello";
char str2[50]
= "World";
char str3[50];
printf("Original
Strings:\n");
printf("str1
= %s\n", str1);
printf("str2
= %s\n\n", str2);
// 1. Length
printf("Length
of str1 = %lu\n", strlen(str1));
// 2. Copy
strcpy(str3,
str1);
printf("After
strcpy, str3 = %s\n", str3);
// 3.
Concatenate
strcat(str1,
str2);
printf("After
strcat, str1 = %s\n", str1);
// 4.
Compare
if(strcmp(str2,
str3) == 0)
printf("str2
and str3 are same\n");
else
printf("str2
and str3 are different\n");
// 5. Reverse
strrev(str1);
printf("Reversed
str1 = %s\n", str1);
// 6.
Uppercase and Lowercase
strupr(str2);
strlwr(str3);
printf("Uppercase
str2 = %s\n", str2);
printf("Lowercase
str3 = %s\n", str3);
return 0;
}
Output:
Original Strings:
str1 = Hello
str2 = World
Length of str1 = 5
After strcpy, str3 = Hello
After strcat, str1 = HelloWorld
str2 and str3 are different
Reversed str1 = dlroWolleH
Uppercase str2 = WORLD
Lowercase str3 = hello
Summary Table
|
Function
|
Meaning
|
Header
|
Example
|
|
strlen()
|
Length of
string
|
<string.h>
|
strlen("Hello")
|
|
strcpy()
|
Copy
string
|
<string.h>
|
strcpy(b,a)
|
|
strcat()
|
Join
strings
|
<string.h>
|
strcat(a,b)
|
|
strcmp()
|
Compare
strings
|
<string.h>
|
strcmp(a,b)
|
|
strrev()
|
Reverse
string
|
<string.h>
|
strrev(a)
|
|
strupr()
|
Convert to
upper
|
<string.h>
|
strupr(a)
|
|
strlwr()
|
Convert to
lower
|
<string.h>
|
strlwr(a)
|
Functions that are Non-Standard- A function that is not defined in the official C standard, but is added by some specific compiler
(like Turbo C) for extra convenience.
|
Function
|
Description
|
Status
|
|
strrev(str)
|
Reverses
string
|
❌
Non-standard
|
|
strupr(str)
|
Converts
to uppercase
|
❌
Non-standard
|
|
strlwr(str)
|
Converts
to lowercase
|
❌
Non-standard
|
6.
Difference Between Character and String
|
Feature
|
Character
|
String
|
|
Definition
|
Single
symbol
|
Group of
characters
|
|
Quotes
|
Single
quotes 'A'
|
Double
quotes "A"
|
|
Size
|
1 byte
|
Many bytes
+ \0
|
|
Library
|
<ctype.h>
|
<string.h>
|
|
End
Character
|
None
|
Must end
with '\0'
|
Palindrome Program (Using String Functions)
