7-1 Find the largest k prime numbers within n and their sum (20 points)
This question requires calculating and outputting the largest k prime numbers and their sums that do not exceed n.
Input format:
Input the values of n(10≤n≤10000) and k(1≤k≤10) given in one line.
Output format: output
in the following format in one line:
Prime number 1+prime number 2+…+prime number k=sum value
The prime numbers are output in descending order. If there are not enough k prime numbers within n, the actual number is output.
Input example 1:
1000 10
Output example 1:
997+991+983+977+971+967+953+947+941+937=9664
Input example 2:
12 6
Output example 2:
11+7+5 +3+2=28
#include <stdio.h>
int main()
{
int n,k,i,j,sum=0,flag=0,x=1,a[]={
0};
scanf("%d%d",&n,&k);
for(i=n;i>1;i--) //因为下面的素数算法有点瑕疵，所以把循环条件设置成i>1
{
for(j=2;j<i;j++)
{
if(i%j!=0) //1不是素数，而这里1是漏网之鱼
flag=1;
else
{
flag=0;
break;
}
}
if(flag)
{
sum+=i;
if(x<=k)
printf("%d",i);
if(x==k || i==2)
{
printf("=%d",sum);
break;
}
else if(i!=2)
printf("+");
x++;
}
}
}