how can i optimize this code for better performance?

The code is to search a word from the string entered. What optimizations can I do to my code and also any other(faster/req. less memory) way I can implement it.

#include <iostream>
#include <string.h>
#include <stdio.h>
using namespace std;

bool possible(char str[], char str_part[]) {
    int len_str = strlen(str);
    int len_part = strlen(str_part);
    if (len_str < len_part)
        return false;
    return true;
}
bool compare(char str[], char str_part[], int pos) {
    int flag = 0;
    for (int i = 0; i < strlen(str_part); ++i) {
        if(str[i+pos] == str_part[i])
            ++flag;
    }
    if (flag == strlen(str_part))
        return true;
    return false;
}
int main(int argc, char* argv) {
    char str[100];
    cout << "enter the string";
    gets(str);
    char str_part[100];
    cout << "enter the string to be searched";
    gets(str_part);
    bool check = possible(str, str_part);
    if (check) {
        for (int i = 0; i < strlen(str);++i ){
            if(str[i] == str_part[0])
                if(compare(str, str_part, i)) {
                    cout << "found it!!";
                    return 0;
                }
        }
    }
    cout << "got nothin";
    return -1;
}

PS:I know about strlen() in for loop so leave that one :)