What are character analysis function, explain with C program?

Character analysis functions in C are predefined functions in the ctype.h library used for analyzing and categorizing character input. These functions help determine the type of character (alphabet, digit, space, etc.) and convert between uppercase and lowercase letters.

Syntax

#include <ctype.h>

int isalpha(int c);
int isdigit(int c);
int isupper(int c);
int islower(int c);
int toupper(int c);
int tolower(int c);

Character Analysis Functions

Character Conversion Functions

Example: Character Analysis and Conversion

Here's a comprehensive program demonstrating various character analysis and conversion functions −

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

int main() {
    char ch1 = 'A';
    char ch2 = '7';
    char ch3 = '@';
    char ch4 = ' ';
    char ch5 = 'z';
    
    printf("Character Analysis:<br>");
    printf("Character '%c': ", ch1);
    if (isalpha(ch1)) printf("alphabet ");
    if (isupper(ch1)) printf("uppercase ");
    printf("<br>");
    
    printf("Character '%c': ", ch2);
    if (isdigit(ch2)) printf("digit ");
    if (isalnum(ch2)) printf("alphanumeric ");
    printf("<br>");
    
    printf("Character '%c': ", ch3);
    if (ispunct(ch3)) printf("punctuation ");
    printf("<br>");
    
    printf("Character '%c': ", ch4);
    if (isspace(ch4)) printf("whitespace ");
    printf("<br>");
    
    printf("\nCharacter Conversion:<br>");
    printf("'%c' to uppercase: '%c'<br>", ch5, toupper(ch5));
    printf("'%c' to lowercase: '%c'<br>", ch1, tolower(ch1));
    
    return 0;
}

Character Analysis:
Character 'A': alphabet uppercase 
Character '7': digit alphanumeric 
Character '@': punctuation 
Character ' ': whitespace 

Character Conversion:
'z' to uppercase: 'Z'
'A' to lowercase: 'a'

Example: String Character Analysis

This example analyzes each character in a string −

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

int main() {
    char str[] = "Hello123!";
    int alpha = 0, digit = 0, punct = 0;
    
    printf("String: %s<br>", str);
    printf("Character breakdown:<br>");
    
    for (int i = 0; i < strlen(str); i++) {
        printf("'%c' - ", str[i]);
        if (isalpha(str[i])) {
            printf("alphabet");
            alpha++;
        } else if (isdigit(str[i])) {
            printf("digit");
            digit++;
        } else if (ispunct(str[i])) {
            printf("punctuation");
            punct++;
        }
        printf("<br>");
    }
    
    printf("\nSummary: %d alphabets, %d digits, %d punctuation marks<br>", 
           alpha, digit, punct);
    
    return 0;
}

String: Hello123!
Character breakdown:
'H' - alphabet
'e' - alphabet
'l' - alphabet
'l' - alphabet
'o' - alphabet
'1' - digit
'2' - digit
'3' - digit
'!' - punctuation

Summary: 5 alphabets, 3 digits, 1 punctuation marks

Key Points

• All ctype.h functions return non-zero (true) if condition is met, zero (false) otherwise.
• Conversion functions return the converted character, or original character if no conversion is possible.
• These functions work with single characters, not strings directly.

Conclusion

Character analysis functions from ctype.h provide efficient ways to classify and convert characters in C. They are essential for text processing, input validation, and string manipulation tasks.