OAIP/21-22/22.c

#include "stdio.h"
#include "string.h"
#include "Windows.h"

int mystrlen(char[]), mystrlenpoint(char*);
int mystrcmp(char[], char[]), mystrcmppoint(char*, char*);
void mystrcpy(char*, char*);
void mystrcat(char*, char*);
void mystrcpyn(char*, char*, int);

int main() {
	char str[100];
	char str1[100];
	int n;

	printf("cpyn\n");
	scanf_s(" %[^\n]", &str1, 100);
	scanf_s("%d", &n);
	mystrcpyn(&str, &str1, n);
	printf("1 = %s, 2 = %s\n", str, str1);

	printf("len\n");
	scanf_s(" %[^\n]", &str, 100);
	printf("len = %d\n", mystrlen(str));

	printf("len pointer\n");
	scanf_s(" %[^\n]", &str, 100);
	printf("len pointer = %d\n", mystrlenpoint(&str));

	printf("cmp\n");
	scanf_s(" %[^\n]", &str, 100);
	scanf_s(" %[^\n]", &str1, 100);
	printf("str - str1 = %d\n", mystrcmp(str, str1));


	printf("cmp pointer\n");
	scanf_s(" %[^\n]", &str, 100);
	scanf_s(" %[^\n]", &str1, 100);
	printf("str - str1 = %d\n", mystrcmppoint(&str, &str1));

	printf("cpy\n");
	scanf_s(" %[^\n]", &str1, 100);
	mystrcpy(str, str1);
	printf("1 = %s, 2 = %s\n", str, str1);

	printf("cat\n");
	scanf_s(" %[^\n]", &str, 100);
	scanf_s(" %[^\n]", &str1, 100);
	mystrcat(str, str1);
	printf("%s", str);
	

	return 0;
}

int mystrlen(char c[]) {
	int k = 0;
	for (int i = 0; c[i] != '\0'; i++) k++;
	return k;
}

int mystrlenpoint(char *c) {
	char* p = c;
	while (*p++);
	return p - c - 1;
}

int mystrcmp(char f[], char s[]) {
	int i;
	for (i = 0; f[i] != '\0' && s[i] != "\0"; i++) {
		if (f[i] - s[i] != 0) break;
	}
	return f[i] - s[i];
}

int mystrcmppoint(char *f, char *s) {
	int i;
	for (i = 0; f[i] != '\0' && s[i] != "\0"; i++) {
		if (f[i] - s[i] != 0) break;
	}
	return f[i] - s[i];
}

void mystrcpy(char *f, char *s) {
	while (*f++ = *s++);
}

void mystrcat(char* f, char* s) {
	while (*f) *f++;
	while (*f++ = *s++);
}

void mystrcpyn(char* f, char* s, int n) {
	int i = 0;
	for (i = 0; s[i] != '\0' && i < n; i++) {
		f[i] = s[i];
	}
	f[i] = '\0';
}