C语言实现 字符串过滤并修改并返回个数

#include <stdlib.h>
#include <stdio.h>
#include <string.h> // 用来测试，输入数据用的，题目要求不能使用库函数

int filter(char *strContent, char *strWord)
{
    int count = 0;
    char *p = strContent;
    char *s = strWord;
    if (p == NULL || s == NULL)
        exit(1);    
    while(*p != ‘\0‘)
    {
        char *p1 = p;
        s = strWord;
        for(;*p1 == *s && *s!= ‘\0‘;p1++,s++);
        if (*s == ‘\0‘)
        {
            count++;
            s = strWord;
            while(*s++ != ‘\0‘) *--p1 = ‘*‘;
        }
        if (*p1 == ‘\0‘)    
        {
            break;
        }    
        p++;
    }
    return count;
}

int main(int argc, char *argv[])
{
    char *strContent = (char *) malloc(20);
    char *strWord = (char *) malloc(20);
    strcpy(strContent, argv[1]);
    strcpy(strWord, argv[2]);
    int result = filter(strContent, strWord);
    printf("result : %d\n", result);
    printf("strContent : %s\n", strContent);
    return 0;
}