Answer:
#pragma is a pre-processor macro in C. It is used to call a function before and after main function in a C program.
<![CDATA[
#include <stdio.h>
void function1( );
void function2( );
#pragma startup function1
#pragma exit function2
int main( )
{
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<small># Tutorial: Introduction about Pre-processor</small>
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<small><i class="fa fa-code" aria-hidden="true"></i> Question: C Pre-processor</small>
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<h5 class="mb-1" style="color:#194757;">665. How will you override an existing macro in C?</h5>
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Answer: <p>To override an existing macro, we need to undefine existing macro using “#undef”. Then, we need to define same macro again with new value.</p> </div>
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<small># Tutorial: Introduction about Pre-processor</small>
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<h5 class="mb-1" style="color:#194757;">666. How to check whether macro is defined or not in a C program?</h5>
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Answer: <p>#ifdef pre-processor directive checks whether particular macro is defined or not in a C program.</p> </div>
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