如下

#include <stdio.h>

int main()
{
	int a[11], b[11];
	float c = 0;
	for (int i = 0; i <= 11; i++)
	{
		scanf("%d", &a[i]);
	}
	for (int j = 0; j <= 11; j++)
	{
		if (j == 0)
		{
			b[j] = 300 - a[j];
		}
		else
		{
			b[j] = 300 + b[j - 1] - a[j];
			if (b[j] < 0)
			{
				printf("-%d", (j + 1));
				return 0;
			}
			else if (b[j] / 100 != 0)
			{
				c = c + (b[j] / 100 * 100);
				b[j] = b[j] - (b[j] / 100 * 100);
			}
			else
			{
				continue;
			}
		}
	}
	printf("%f", b[11] + c + c * 0.2);
	return 0;
}