Linux_C练习:判断一个字符串是不是另一个字符串的子串；（比如"ab"是"aabcd"的子串）

#include<stdio.h>
#include<stdlib.h>
#include<string.h>

int com(char *p, char *q, int n, int m)
{
int i, j;
char *tmp = (char *)malloc(sizeof(char) * 20);
if(NULL == tmp)
{
printf("error\n");
exit(1);
}
char *tmp1 = tmp;
char *tmp2 = q;
char *tmp3 = p;
int flag = 0;
if(n < m)
{
for(i = 0; i <= m - n; ++i )
{
q = q + i;
for(j = i; j< i + n; ++j)
{

*tmp++ = *q++;
}
tmp = tmp1;
if(strcmp(tmp, p) == 0)
{
flag = 1;
}
q = tmp2;
}

}
if(n > m)
{
for(i = 0; i <= n - m; ++i )
{
p = p + i;
for(j = i; j< i + m; ++j)
{

*tmp++ = *p++;
}
tmp = tmp1;
if(strcmp(tmp,q) == 0)
{
flag = 2;
}
p = tmp3;
}

}
if(n == m)
{
if(strcmp(p, q) == 0)
{
flag = 3;
}
}
return flag;
}

int main()
{
int l, l1;
char *p = (char *)malloc(sizeof(char) * 20);
char *q = (char *)malloc(sizeof(char) * 20);
int flag;
if(NULL == p || NULL == q)
{
printf("NULL error\n");
exit(1);
}
printf("请输入第一个字符串\n");
scanf("%s", p);
printf("请输入第二个字符串\n");
scanf("%s", q);
l = strlen(p);
l1 = strlen(q);
flag = com(p, q, l, l1);
switch(flag)
{
case 0: printf("两字符串互不为对方的子串\n");
break;
case 1: printf("第一个字符串为第二个的子串\n");
break;
case 2: printf("第二个字符串为第一个的子串\n");
break;
case 3: printf("互为子串\n");
break;
default: printf("111\n");
break;
}
return 0;
}