C++ Program to Check Whether a Character is Alphabet or Not

Using strings or characters is sometimes very useful while solving some logical programming problems. Strings are a collection of characters and characters are 1-byte datatype to hold symbols from ASCII values. The symbols can be letters from English alphabets, numeric digits, or special characters. In this article, we shall learn how to check whether a character is a letter in English an alphabet or not using C++.

Checking isalpha() function

To check whether a number is an alphabet or not, we can use the isalpha() function from the ctype.h header file. This takes a character as input and returns true when it is the alphabet, otherwise returns false. Let us see the following C++ implementation to understand the usage of this function.

Example

<div class="execute"></div><div class="code-mirror  language-cpp" contenteditable="plaintext-only" spellcheck="false" style="outline: none; overflow-wrap: break-word; overflow-y: auto; white-space: pre-wrap;"><span class="token macro property"><span class="token directive-hash">#</span><span class="token directive keyword">include</span> <span class="token string"><iostream></span></span>
<span class="token macro property"><span class="token directive-hash">#</span><span class="token directive keyword">include</span> <span class="token string"><ctype.h></span></span>
<span class="token keyword">using</span> <span class="token keyword">namespace</span> std<span class="token punctuation">;</span>
string <span class="token function">solve</span><span class="token punctuation">(</span> <span class="token keyword">char</span> c <span class="token punctuation">)</span> <span class="token punctuation">{</span>
   <span class="token keyword">if</span><span class="token punctuation">(</span> <span class="token function">isalpha</span><span class="token punctuation">(</span> c <span class="token punctuation">)</span> <span class="token punctuation">)</span> <span class="token punctuation">{</span>
      <span class="token keyword">return</span> <span class="token string">"True"</span><span class="token punctuation">;</span>
   <span class="token punctuation">}</span>
   <span class="token keyword">else</span> <span class="token punctuation">{</span>
      <span class="token keyword">return</span> <span class="token string">"False"</span><span class="token punctuation">;</span>
   <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
<span class="token keyword">int</span> <span class="token function">main</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
<span class="token punctuation">{</span>
   cout <span class="token operator"><<</span> <span class="token string">"Is 'K' an alphabet? : "</span> <span class="token operator"><<</span> <span class="token function">solve</span><span class="token punctuation">(</span> <span class="token string">'K'</span> <span class="token punctuation">)</span> <span class="token operator"><<</span> endl<span class="token punctuation">;</span>
   cout <span class="token operator"><<</span> <span class="token string">"Is 'a' an alphabet? : "</span> <span class="token operator"><<</span> <span class="token function">solve</span><span class="token punctuation">(</span> <span class="token string">'a'</span> <span class="token punctuation">)</span> <span class="token operator"><<</span> endl<span class="token punctuation">;</span>
   cout <span class="token operator"><<</span> <span class="token string">"Is '!' an alphabet? : "</span> <span class="token operator"><<</span> <span class="token function">solve</span><span class="token punctuation">(</span> <span class="token string">'!'</span> <span class="token punctuation">)</span> <span class="token operator"><<</span> endl<span class="token punctuation">;</span>
   cout <span class="token operator"><<</span> <span class="token string">"Is '5' an alphabet? : "</span> <span class="token operator"><<</span> <span class="token function">solve</span><span class="token punctuation">(</span> <span class="token string">'5'</span> <span class="token punctuation">)</span> <span class="token operator"><<</span> endl<span class="token punctuation">;</span>
   cout <span class="token operator"><<</span> <span class="token string">"Is 'f' an alphabet? : "</span> <span class="token operator"><<</span> <span class="token function">solve</span><span class="token punctuation">(</span> <span class="token string">'f'</span> <span class="token punctuation">)</span> <span class="token operator"><<</span> endl<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</div><div class="output-wrapper"><div class="console-close"></div><div class="code-output"></div></div>

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 function for checking

The above-mentioned method is using a predefined function that checks whether the given character is an alphabet or not. But the same thing we can implement by defining a function with ranging conditions. The algorithm is given below ?

Algorithm

• read a character c as input
• if ASCII of c is in range lowercase 'a' and 'z' or in range uppercase 'A' and 'Z', then
• otherwise
• return false
• end if

Example

<div class="execute"></div><div class="code-mirror  language-cpp" contenteditable="plaintext-only" spellcheck="false" style="outline: none; overflow-wrap: break-word; overflow-y: auto; white-space: pre-wrap;"><span class="token macro property"><span class="token directive-hash">#</span><span class="token directive keyword">include</span> <span class="token string"><iostream></span></span>
<span class="token macro property"><span class="token directive-hash">#</span><span class="token directive keyword">include</span> <span class="token string"><ctype.h></span></span>

<span class="token keyword">using</span> <span class="token keyword">namespace</span> std<span class="token punctuation">;</span>
string <span class="token function">solve</span><span class="token punctuation">(</span> <span class="token keyword">char</span> c <span class="token punctuation">)</span> <span class="token punctuation">{</span>
   <span class="token keyword">if</span><span class="token punctuation">(</span> <span class="token punctuation">(</span>c <span class="token operator">>=</span> <span class="token string">'a'</span> <span class="token operator">&&</span> c <span class="token operator"><=</span> <span class="token string">'z'</span><span class="token punctuation">)</span> <span class="token operator">||</span> <span class="token punctuation">(</span>c <span class="token operator">>=</span> <span class="token string">'A'</span> <span class="token operator">&&</span> c <span class="token operator"><=</span> <span class="token string">'Z'</span><span class="token punctuation">)</span> <span class="token punctuation">)</span> <span class="token punctuation">{</span>
      <span class="token keyword">return</span> <span class="token string">"True"</span><span class="token punctuation">;</span>
   <span class="token punctuation">}</span>
   <span class="token keyword">else</span> <span class="token punctuation">{</span>
      <span class="token keyword">return</span> <span class="token string">"False"</span><span class="token punctuation">;</span>
   <span class="token punctuation">}</span>
<span class="token punctuation">}</span>

<span class="token keyword">int</span> <span class="token function">main</span><span class="token punctuation">(</span><span class="token punctuation">)</span>
<span class="token punctuation">{</span>
   cout <span class="token operator"><<</span> <span class="token string">"Is 'T' an alphabet? : "</span> <span class="token operator"><<</span> <span class="token function">solve</span><span class="token punctuation">(</span> <span class="token string">'T'</span> <span class="token punctuation">)</span> <span class="token operator"><<</span> endl<span class="token punctuation">;</span>
   cout <span class="token operator"><<</span> <span class="token string">"Is 'g' an alphabet? : "</span> <span class="token operator"><<</span> <span class="token function">solve</span><span class="token punctuation">(</span> <span class="token string">'g'</span> <span class="token punctuation">)</span> <span class="token operator"><<</span> endl<span class="token punctuation">;</span>
   cout <span class="token operator"><<</span> <span class="token string">"Is '?' an alphabet? : "</span> <span class="token operator"><<</span><span class="token function">solve</span><span class="token punctuation">(</span> <span class="token string">'?'</span> <span class="token punctuation">)</span> <span class="token operator"><<</span> endl<span class="token punctuation">;</span>
   cout <span class="token operator"><<</span> <span class="token string">"Is '8' an alphabet? : "</span> <span class="token operator"><<</span> <span class="token function">solve</span><span class="token punctuation">(</span> <span class="token string">'8'</span> <span class="token punctuation">)</span> <span class="token operator"><<</span> endl<span class="token punctuation">;</span>
   cout <span class="token operator"><<</span> <span class="token string">"Is 'p' an alphabet? : "</span> <span class="token operator"><<</span> <span class="token function">solve</span><span class="token punctuation">(</span> <span class="token string">'p'</span> <span class="token punctuation">)</span> <span class="token operator"><<</span> endl<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</div><div class="output-wrapper"><div class="console-close"></div><div class="code-output"></div></div>

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

Conclusion

Checking whether a given character is an alphabet or not, there are a few different methods. The very first method we have discussed is using the isalpha function from ctype.h header file. This will take a character, when it is an alphabet, returns true, otherwise false. In the second method that we have covered, we are writing our function for this checking. This is being checked by checking the ASCII is within the given range of lowercase ?a? to ?z? or uppercase ?A? to ?Z?. If yes, then return true, otherwise false.