Символьные строки и функции над ними

Определение: 
char *strrchr(s,c)
char *s;
int c;

#include <string.h>
#include <stdio.h>
#include <conio.h>
int main(void)
{
clrscr();
	char string[20];
	char *ptr, c = 'r';
	strcpy(string, "This is a string");
	ptr = strrchr(string, c);
	if (ptr)
		printf("The character %c is at position: %d\n", c, *ptr);
	else
		printf("The character was not found\n");
		getch();
	return 0;
}

Определение: 
char *strpbrk(s1,s2)
char *s1, *s2;

#include <stdio.h>
#include <string.h>
#include <conio.h>
int main(void)
{
	clrscr();
	char *string1 = "abcdefghijklmnopqrstuvwxyz";
	char *string2 = "onm";
	int *ptr;
	ptr = strpbrk(string1, string2);
	if (ptr)
		printf("strpbrk found first character: %c\n", *ptr);
	else
		printf("strpbrk didn't find character in set\n");
	getch();
return 0;
}

Определение: 
int strspn(s1,s2)
char *s1, *s2;

#include <stdio.h>
#include <string.h>
#include <alloc.h>
#include <conio.h>
int main(void)
{
	clrscr();
	char *string1 = "1234567890";
	char *string2 = "123DC8";
	int length;
	length = strspn(string1, string2);
	printf("Character where strings differ is at position %d\n", length);
	getch();
	return 0;
}

Определение: 
int strcspn(s1,s2)
char *s1, *s2;

#include <stdio.h>
#include <string.h>
#include <alloc.h>
#include <conio.h>
int main(void)
{
	clrscr();
	char *string1 = "1234567890";
	char *string2 = "747DC8";
	int length;
	length = strcspn(string1, string2);
	printf("Character where strings intersect is at position %d\n", length);
	getch();
	return 0;
}

Определение: 	char *strtok(s1,s2) 
char *s1, *s2;

#include <string.h>
#include <stdio.h>
#include <conio.h>
int main(void)
{
clrscr();
	char input[16] = "abc,d";
	char *p;
	p = strtok(input, ",");
	if (p) printf("%s\n", p);
	p = strtok(NULL, ",");
	if (p)   printf("%s\n", p);
	getch();
	return 0;
}