C Program - Write a program to check whether a number is a prime number or not.(Using While loop)

C Programming Language Loop control in C Language (Article) Loop control in C Language (Program)

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If you don't know what is prime number please read form this tutorial. Prime Number & Prime Factors

Program:

<span class="com">#include</span><span class="pln"> </span><span class="str">&lt;stdio.h&gt;</span><span class="pln">
</span><span class="kwd">int</span><span class="pln"> main</span><span class="pun">(</span><span class="pln"> </span><span class="pun">)</span><span class="pln">
</span><span class="pun">{</span><span class="pln">
	</span><span class="kwd">int</span><span class="pln"> n</span><span class="pun">,</span><span class="pln"> r</span><span class="pun">,</span><span class="pln"> d</span><span class="pun">=</span><span class="lit">2</span><span class="pun">;</span><span class="pln">
	printf</span><span class="pun">(</span><span class="pln"> </span><span class="str">"\n Enter the number :"</span><span class="pun">);</span><span class="pln">
	scanf</span><span class="pun">(</span><span class="str">"%d"</span><span class="pun">,</span><span class="pln"> </span><span class="pun">&amp;</span><span class="pln">n</span><span class="pun">);</span><span class="pln">
	r </span><span class="pun">=</span><span class="pln"> </span><span class="lit">1</span><span class="pun">;</span><span class="pln">
	</span><span class="kwd">while</span><span class="pun">(</span><span class="pln">d </span><span class="pun">&lt;=</span><span class="pln"> n</span><span class="pun">/</span><span class="lit">2</span><span class="pun">)</span><span class="pln">
	</span><span class="pun">{</span><span class="pln">
		r </span><span class="pun">=</span><span class="pln"> n</span><span class="pun">%</span><span class="pln">d</span><span class="pun">;</span><span class="pln">
		</span><span class="kwd">if</span><span class="pun">(</span><span class="pln">r </span><span class="pun">==</span><span class="pln"> </span><span class="lit">0</span><span class="pun">)</span><span class="pln">
			</span><span class="kwd">break</span><span class="pun">;</span><span class="pln">
		d</span><span class="pun">++;</span><span class="pln">
	</span><span class="pun">}</span><span class="pln">
	</span><span class="kwd">if</span><span class="pun">(</span><span class="pln">r</span><span class="pun">==</span><span class="lit">0</span><span class="pun">)</span><span class="pln">
		printf</span><span class="pun">(</span><span class="str">"\n IT IS NOT A PRIME NUMBER"</span><span class="pun">);</span><span class="pln">
	</span><span class="kwd">else</span><span class="pln">
		printf</span><span class="pun">(</span><span class="str">"\n IT IS A PRIME NUMBER"</span><span class="pun">);</span><span class="pln">
		
	getch</span><span class="pun">();</span><span class="pln">	
	</span><span class="kwd">return</span><span class="pln"> </span><span class="lit">0</span><span class="pun">;</span><span class="pln">
</span><span class="pun">}</span>

Output:

 Output 1:  

Enter the number :5

 IT IS A PRIME NUMBER



 Output 2: 

 Enter the number :12

 IT IS NOT A PRIME NUMBER 

Explanation:

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