Consider the given example, here I wrote mian() instead of main(), see the spelling of main() which is not correct in the program.

Example:

#include <stdio.h>

int mian(void) {
	printf("Hello world!");
	return 0;
}

Output

/usr/lib/gcc/x86_64-linux-gnu/6/../../../x86_64-linux-gnu/Scrt1.o: In function '_start':
(.text+0x20): undefined reference to 'main'
collect2: error: ld returned 1 exit status

How to fix?

To fix this error, correct the spelling of the main() function.

Correct code:

#include <stdio.h>

int main(void) {
	printf("Hello world!");
	return 0;
}

Output

Hello world!