C语言问题不知道就问不会做

#include "stdio.h"

int main(){
    int i;
    int cnt=0;
    for(i = 100;i<=100;i++){
        if(i % 4==0 && i%7==0){
            cnt++;
            printf("%d\t",i);
            if(cnt<=20 && cnt %10==0){
                printf("\n");
            }else if(cnt % 5==0){
                printf("\n");
            }
        }
    }

    return 0;
}

题目1：

#include <iostream>
#include <iomanip>
using namespace std;
int main()
{
	double lr = 0;
	double jiangjin = 0;
	cout << "请输入当月利润:" ;
	cin >> lr;
	if (lr <= 5)
	{
		jiangjin = lr * 0.05;
	}else if(lr > 5 < 10)
	{
		jiangjin = 5 * 0.1 + (lr - 5) * 0.08;
	}else if(lr >= 10 && lr < 20)
		jiangjin = 5*0.1 + 5*0.08 + (lr -10)*0.06;
	else if(lr >= 20 && lr < 30)
		jiangjin = 5*0.1 + 5*0.08 + 10* 0.06 + (lr -20)*0.05;
	else if(lr >= 30 && 50)
		jiangjin = 5*0.1 + 5*0.08 + 10* 0.06 + 10*0.05 + (lr - 30)*0.03;
	else 
		jiangjin = 5*0.1 + 5*0.08 + 10* 0.06 + 10*0.05 + 20*0.03 +(lr-50)*0.015;
	cout << "奖金数:" << fixed << setprecision(3) << jiangjin << endl;
	return 0;
}

题目2：

#include <iostream>
using namespace std;
int main()
{
	int i;
	int nmb = 0;

	for (i = 100; i <=1000;i++)
	{
		if( (i%7 == 0) && (i%4==0) )
		{
			cout << i << " ";
			nmb++;
			if( (nmb == 10) || (nmb == 20) )
				cout << endl;
			else if ( (nmb > 20) && (nmb%5 == 0))
			{
				cout << endl;
			}
		}
		
	}
	
	return 0;
}

题目3：

#include <iostream>
using namespace std;
int main()
{
	int i;
	int arr[10];
	int zs = 0;
	int fs = 0;
	int zero = 0;
	cout << "请输入10个整数:";
	for (i = 0;i<10;i++)
	{
		cin >> arr[i];
		if(arr[i] > 0)
			zs++;
		else if(arr[i] == 0)
			zero++;
		else
			fs++;
	}
	cout << "正数:" << zs << endl;
	cout << "负数:" << fs << endl;
	cout << "零:" << zero << endl;
	
	return 0;
}

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