At programming c / c you often encounter drift phenomenon command (fails to enter data). To remedy this situation, you use the ffulsh(stdin) to clear the buffer. But on Linux does not have this function, please replace it with the command

__fpurge(stdin);

Code examples:

#include <stdio.h>	// io
#include <stdio_ext.h> // __fpurge(stdin);
int main() {
	int x;
	char s[100];
	
	// scan a number
	printf("enter number x = ");
	scanf("%d", &x);
	
	// clear stdin
	__fpurge(stdin);
	
	// scan a string
	printf("enter a string: ");
	gets(s);
	
	printf("number is %d \nstring is %s\n", x,s);
	return 0;
}

enter number x = 7826
enter a string: nguyen van quan
number is 7826 
string is nguyen van quan

Read more gets() and fget() in C/C