C - Character Manipulation Functions

Introduction

C has functions to test or manipulate individual characters.

The functions are all defined in the ctype.h header file.

To use the CTYPE functions, the ctype.h header file must be included in your source code:

#include <ctype.h> 

CTYPE functions are of two categories: testing and manipulation.

The following table lists testing functions.

Function
Returns TRUE When ch is
isalnum(ch)
A letter of the alphabet (upper- or lowercase) or a number
isalpha(ch)
An upper- or lowercase letter of the alphabet
isascii(ch)
An ASCII value in the range of 0 through 127
isblank(ch)
A tab or space or another blank character
iscntrl(ch)
A control code character, values 0 through 31 and 127
isdigit(ch)
A character 0 through 9
isgraph(ch)
Any printable character except for the space
ishexnumber(ch)

Any hexadecimal digit, 0 through 9 or A through F (upper-
or lowercase)
islower(ch)
A lowercase letter of the alphabet, a to z
isnumber(ch)
See isdigit()
isprint(ch)
Any character that can be displayed, including the space
ispunct(ch)
A punctuation symbol
isspace(ch)

A white-space character, space, tab, form feed, or an
Enter, for example
isupper(ch)
An uppercase letter of the alphabet, A to Z
isxdigit(ch)
See ishexnumber()

manipulation functions.

toascii(ch) The ASCII code value of ch, in the range of 0 through 127
tolower(ch) The lowercase of character ch
toupper(ch) The uppercase of character ch

Generally speaking, testing functions begin with is, and conversion functions begin with to.

Every CTYPE function accepts an int value as the argument.

Every CTYPE function returns an int value.

Demo

#include <stdio.h> 
#include <ctype.h> 

int main() //from   ww w. j a  v  a2s.  co  m
{ 
    char phrase[] = "this is a test."; 

       int index,alpha,blank,punct; 

       alpha = blank = punct = 0; 

    /* gather data */ 
       index = 0; 
       while(phrase[index]) 
       { 
           if(isalpha(phrase[index])) 
               alpha++; 
           if(isblank(phrase[index])) 
               blank++; 
           if(ispunct(phrase[index])) 
               punct++; 
           index++; 
       } 

    /* print results */ 
       printf("\"%s\"\n",phrase); 
       puts("Statistics:"); 
       printf("%d alphabetic characters\n",alpha); 
       printf("%d blanks\n",blank); 
       printf("%d punctuation symbols\n",punct); 

       return(0); 
    }

Result

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