字符串剪切复制

//a是一个字符数组，含有n个字符，把字符串a的m个字符以后的部分变为字符串b
#include <stdio.h>

//判断字符串长度
int len_str(char *poiter)
{
	int n = 0;
	int i = 0;
	do{
		n++;
		i++;
	}while (*(poiter+i) != NULL);
	
	return n;

}


char new_str(int m, char *p1, char *p2)
{
	int i;
	for (i = 0; i < m; i++){
		p1++;

	}
	while(*p2 != NULL){
		*p1 = *p2;
		p2++;
		p1++;
	}
	*p1 = NULL;
	return 0;
}


void main ()
{
	int n;
	char *poiter;
	char a[128];
	int m;
	char b[] = "china";
	poiter = a;

	printf ("input a string : ");
	scanf ("%s", poiter);
	printf ("%s\n", poiter);
	n = len_str(poiter);
	m = len_str(b);

	if (n > m){
		
	new_str(m, a, b);
	}else ("input error");

	printf("the new string is : %s\n", a);
}