C++ program to check if a character is alphabetic or non-alphabetic

Using strings or characters is sometimes very useful when solving some logic programming problems. A string is a collection of characters, a 1-byte data type that holds symbols in ASCII values. Symbols can be English letters, numbers, or special characters. In this article, we will learn how to check if a character is an English letter or a letter of the alphabet using C.

Check isalpha() function

To check if a number is a letter, we can use the isalpha() function in the ctype.h header file. This takes a character as input and returns true if it is an alphabet, false otherwise. Let us look at the following C implementation to understand the usage of this function.

The Chinese translation of

Example

is:

Example

#include <iostream>
#include <ctype.h>
using namespace std;
string solve( char c ) {
   if( isalpha( c ) ) {
      return "True";
   }
   else {
      return "False";
   }
}
int main()
{
   cout << "Is 'K' an alphabet? : " << solve( 'K' ) << endl;
   cout << "Is 'a' an alphabet? : " << solve( 'a' ) << endl;
   cout << "Is '!' an alphabet? : " << solve( '!' ) << endl;
   cout << "Is '5' an alphabet? : " << solve( '5' ) << endl;
   cout << "Is 'f' an alphabet? : " << solve( 'f' ) << endl;
}

Output

Is 'K' an alphabet? : True
Is 'a' an alphabet? : True
Is '!' an alphabet? : False
Is '5' an alphabet? : False
Is 'f' an alphabet? : True

By creating our check function

The above method is to use a predefined function to check whether a given character is a letter. But we can also achieve the same functionality by defining a function with range conditions. The algorithm is as follows -

algorithm

• Read character c as input
• If the ASCII of c is in the range of lowercase "a" and "z" or in the range of uppercase "A" and "Z", then
• otherwise
• Return error
• If it ends

The Chinese translation of

Example

is:

Example

#include <iostream>
#include <ctype.h>

using namespace std;
string solve( char c ) {
   if( (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') ) {
      return "True";
   }
   else {
      return "False";
   }
}

int main()
{
   cout << "Is 'T' an alphabet? : " << solve( 'T' ) << endl;
   cout << "Is 'g' an alphabet? : " << solve( 'g' ) << endl;
   cout << "Is '?' an alphabet? : " <<solve( '?' ) << endl;
   cout << "Is '8' an alphabet? : " << solve( '8' ) << endl;
   cout << "Is 'p' an alphabet? : " << solve( 'p' ) << endl;
}

Output

Is 'T' an alphabet? : True
Is 'g' an alphabet? : True
Is '?' an alphabet? : False
Is '8' an alphabet? : False
Is 'p' an alphabet? : True

in conclusion

There are several different ways to check if a given character is a letter. The first method we discussed is to use the isalpha function in the ctype.h header file. This function returns true when the character is a letter, false otherwise. In the second method we discussed, we wrote our own function to do this check. This is done by checking if the ASCII code is within a given range of lowercase letters 'a' to 'z' or uppercase letters 'A' to 'Z'. If so, it returns true, otherwise it returns false.

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