long iSeconds;
    cout << "来个以秒为单位的数字" << endl;
    cin >> iSeconds;
    int days = iSeconds / (24 * 60 * 60);
    int hours = (iSeconds % (24 * 60 * 60)) / (60 * 60);
    int minutes = (iSeconds % (60 * 60)) / 60;
    int seconds = iSeconds % 60;
    printf("来了，%d天%d小时%d分钟%d秒\n", days, hours, minutes, seconds);
    cout << days * 24 * 60 * 60 + hours * 60 * 60 + minutes * 60 + seconds;

练习2修改

#include "pch.h"
#include <iostream>
#include "stdio.h"
using namespace std;
int main()
{
	int s, d, h, m;;
	cout << "请输入秒数" << endl;
	cin >> s;
	d = s / (60 * 60 * 24);
	h = (s - d * 60 * 60 * 24) / (60 * 60);
	m = (s - h * 60 * 60 - d * 60 * 60 * 24) / 60;
	s = s - d * 60 * 60 * 24 - h * 60 * 60 - m * 60;
	cout << "其中包含" << d << "天" << h << "小时" << m << "分钟" << s << "秒" << endl;
	cin.get();
}

练习3修改

#include "pch.h"
#include <iostream>
#include "stdio.h"
using namespace std;
int main()
{
	int m,f,p;
	cout << "请输入男生人数"<<endl;
	cin >> m;
	cout << "请输入女生人数"<<endl;
	cin >> f;
	p = (f /float (m + f))*100;
	cout << "女生比例为"<<p<<"%"<<endl;
	return 0;

}

int girlsNumber;
    int boysNumber;
    int total;
    cout << "请输入女生数量：";
    cin >> girlsNumber;
    cout << "请输入男生数量：";
    cin >> boysNumber;
    total = girlsNumber + boysNumber;
    int percent = (girlsNumber / float(total)) * 100;//把这个小数乘以100就是百分比          这里total使用了强制类型转换
    cout << percent << "%" << endl;