why do i get Time limit exceeded :(

#include <cstring>
#include <cstdlib>
#include <cstdio>
using namespace std;

int main ()
{
    char * pch;
    char str[30005],str1[30005];
    int number,i=0,j=0;
    scanf("%d",&number);
    while(i<number)
    {
    scanf("%s",str);
    i+=strlen(str);
    strcat(str1,str);
    }
    while(strstr(str1,"><"))
    {
        pch=strstr(str1,"><");
        strncpy(pch,"<>",2);
        j++;
    }

        printf("%d",j);
  return 0;
}

I used very similar code and got AC (though there is a better solution if I recall correctly). What I did is:
- If you have <<< at left end or >>> at right and, you can ignore those - they will never change again. Thus, you can keep treack of the left and right endings, and only parse those, instead of going from 0 to n every time.

AC 0.625

#include <iostream>
using namespace std;
int main()
{
    int n;
    cin >> n;
    char c;
    int t = 0, ans = 0;
    while (n--)
    {
        cin >> c;
        if (c == '>')
            ++t;
        else
            ans += t;
    }
    cout << ans << endl;
    return 0;
}