What is a #error directive in c programming language?

Answer: Syntax: #error If compiler compiles this line then it shows a compiler fatal error i.e. it only issue an error message and this error message includes. I.e. it only issues an error message and this error message includes. e.g.:   #ifndef __MATH_H #error First include then compile #else void main() { float a,b=25; a=sqrt(b); printf(“%f”,a); } #endif Output: compiler error -