1求出1-100之間的素數
#include<stdio.h>
int main()
{
int i;
int j;
int flag = 0;
int count = 0;
for(i = 2;i < 100;i++)
{
for(j = 2;j <= i / 2;j++)
{
if(i % j == 0)
{
flag = 1;
break;
}
}
if(flag == 0)
{
count ++;
printf("%d\t",i);
}
flag = 0;
}
printf("\n");
printf("the count = %d\n",count);
return 0;
}
2求1=1000之間的完數
#include <stdio.h>
int main()
{
int i;
int j;
int sum = 0;
int num = 0;
for(i = 1;i < 1000;i++)
{
for(j = 1;j < i;j++)
{
if( i % j == 0)
sum += j;
}
if(sum == i)
{
num++;
printf("%d\n",i);
}
sum = 0;
}
printf("\n");
printf("the number is %d\n",num);
return 0;
}
3、求1-n之間9的個數
#include <stdio.h>
int main()
{
int i;
int num;
int temp = 0;
int count = 0;
printf("please input a number:\n");
scanf("%d",&num);
for(i = 1;i <= num;i++)
{
temp = i ;
while(temp != 0)
{
if(9 == temp % 10)
{
count++;
}
temp /= 10;
}
}
printf("9 count is %d\n",count);
return 0;
}