help with substring in c programing

#include<stdio.h>
#include<conio.h>

void main()
{
char str[80],sub[10];    
int count1=0,count2=0,i,j,flag;

clrscr();

puts("Enter a string:");
gets(str);

puts("Enter search substring:");
gets(sub);

while (str[count1]!='\0')
count1++;

while (sub[count2]!='\0')
count2++;

for(i=0;i<=count1-count2;i++)
{
for(j=i;j<i+count2;j++)
{
flag=1;
if (str[j]!=sub[j-i])
{
flag=0;
break;
}
}
if (flag==1)
break;
}
if (flag==1)
puts("Substring is found!");
else
puts("Substring does not found!");
getch();
}

thank you for your help, but when I run the program in eclipse, I get the error message " implicit declaration of function clrscr().