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

main(){

	double score, sum = 0, count = 0, passing = 0, passPercentage;

	printf("Enter a test score: (-1 to quit) \n");
	scanf("%lf", &score);
	count = count + 1;
	if(score >= 60 && score <= 100){
			passing = passing + 1;
		}

	if (score > 100 || score <= -2){
		printf("This is not a valid grade! \n");

	}

	while (score != -1) {
		printf("Enter a test score: (-1 to quit) \n");
		scanf("%lf", &score);

		count = count + 1;

		if(score >= 60 && score <= 100){
			passing = passing + 1;
		}
	}

	count = count - 1;

	passPercentage = passing / count * 100;

	printf(" \n Percentage of passing scores: %lf. \n", passPercentage);

	system("pause");

}