Language: C

#include <stdio.h>

void pria(int a, int b, int c, int d);
void prib();
void pric(int c, int d);

int main()
{
	int a, b, c, d;
	while (scanf("%d%d%d%d", &a, &b, &c, &d)!=EOF) {
		if (c>a&&c<b&&d>b) pria(a, b, c, d);
		else if (c>b) prib();
		else pric(c, d);
	}
	return 0;
}

void pria(int a, int b, int c, int d)
{
	printf("%d\n\n", b-c);
	printf("Alice started holding down her button %d second after the start-up of the robot,
and released her button %d second after the start-up.\n", a, b);
	printf("Bob started holding down his button %d second after the start-up, and released his button %d second after the start-up.\n", c, d);
	printf("Therefore, the time when both of them were holding down their buttons, is the %d seconds from %d seconds after the start-up to %d seconds after the start-up.\n", b-c, c, b);
}

void prib()
{
	printf("0\n\n");
	printf("Alice and Bob were not holding their buttons at the same time, so the answer is zero seconds.\n");
}

void pric(int c, int d)
{
	printf("%d\n", d-c);
}

Compiler output:
main.c: In function 'pria':
main.c:21:16: warning: missing terminating " character
   21 |         printf("Alice started holding down her button %d second after the start-up of the robot,
      |                ^
main.c:21:16: error: missing terminating " character
   21 |         printf("Alice started holding down her button %d second after the start-up of the robot,
      |                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
main.c:22:1: error: 'and' undeclared (first use in this function)
   22 | and released her button %d second after the start-up.\n", a, b);
      | ^~~
main.c:22:1: note: each undeclared identifier is reported only once for each function it appears in
main.c:22:4: error: expected ')' before 'released'
   22 | and released her button %d second after the start-up.\n", a, b);
      |    ^~~~~~~~~
      |    )
main.c:21:15: note: to match this '('
   21 |         printf("Alice started holding down her button %d second after the start-up of the robot,
      |               ^
main.c:22:54: error: stray '\' in program
   22 | and released her button %d second after the start-up.\n", a, b);
      |                                                      ^
main.c:22:56: warning: missing terminating " character
   22 | and released her button %d second after the start-up.\n", a, b);
      |                                                        ^
main.c:22:56: error: missing terminating " character
   22 | and released her button %d second after the start-up.\n", a, b);
      |                                                        ^~~~~~~~~
main.c:24:190: error: expected ';' before '}' token
   24 |         printf("Therefore, the time when both of them were holding down their buttons, is the %d seconds from %d seconds after the start-up to %d seconds after the start-up.\n", b-c, c, b);
      |                                                                                                                                                                                              ^
      |                                                                                                                                                                                              ;
   25 | }
      | ~