Challenge #1 Buckys Room - Is password strong or weak

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

/*
Challenge #1 Buckys Room
Is password strong or weak by Goran
*/

int main()
{
    int upperCase = 0, number = 0, dolarSign = 0, loop;
    char password[20], temp; // 20 bytes for storing user password and char temp for storing one character for testing purpose.
    printf("Please enter your password: "); // asking user to enter his password.
    scanf(" %s", password); // gets input from user and stores it into char password.

    for(loop=0; loop<=20; loop++){ // loop that will start at 0, end at 20 and will increment by one.
        temp = password[loop]; // storing one character from user password at a time in char temp for testing.
        if(isupper(temp)){ // if character that we are testing is uppercase letter.
            upperCase++; // increment upperCase integer by one if statement above is true.
        }if(isdigit(temp)){ // if character that we are testing is number.
            number++; // increment number integer by one if statement above is true.
        }if(temp == '$'){ // if character that we are testing is dolar sign.
            dolarSign++; // increment dolarSign integer by one if statement above is true.
        }

    }if(upperCase >= 1 && number >= 1 && dolarSign >= 1){ // password need to have uppercase letter, number and dolar sign to be strong.
        printf("Your password is strong. \n \n"); // if statement above is true it will print out user that password he entered is strong.
    }else{
        printf("Your password is weak. \n \n"); // else if statement above is not true it will print out user that password he entered is weak.
        }

    system("pause"); // pausing program after executing.
    return 0;
}