C #error

#include<stdio.h>
#ifndef __MATH_H
#error First include then compile
#else
void main(){
    float a;
    a=sqrt(7);
    printf("%f",a);
}
#endif

Compile Time Error: First include then compile

#include<stdio.h>
#include<math.h>
#ifndef __MATH_H
#error First include then compile
#else
void main(){
    float a;
    a=sqrt(7);
    printf("%f",a);
}
#endif

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