实现一串字符串的的某一段替换

#include<stdio.h>
#include<string.h>
int input_array(char *ptr)
{
	scanf("%s",ptr);
	getchar();
}

int	str_replace(char* ptra,char *ptrb,char *ptrc)
{
	int reta = 0,retb = 0;
	int i = 0,j= 0,x = 0;
	char* pa = NULL;
	char* pb = NULL;
	reta = strlen(ptra);
	retb = strlen(ptrb);
	for(i=0;i<reta;i++)
	{
		if(*ptra==*ptrb)
		{
			pa=ptra;
			pb=ptrb;
			for(j=1; j<retb; j++)
			{
				if(( *(pa+j) == *(pb+j))&&(j<=(retb-1)))
				{
					for(x =0;x<retb;x++)
					{
						*(ptra+x)=*(ptrc+x);
					}
				}
				else break;

			}
		}
		ptra++;
	}

}
int main(int argc,char *argv[])
{
	int i = 0;
	char a[100] = {0};
	char b[100] = {0};
	char c[100] = {0};
	printf("请输入一串字符串");
	input_array(a);
	printf("请输入要替换的字符串");
	input_array(b);
	printf("请输入目标字符串：");
	input_array(c);
	str_replace(a,b,c);
	for(i=0;i<strlen(a);i++)
	{
		printf("%c",a[i]);
	}
	printf("\n");
	return 0;
}