1.for 循环

#include<stdio.h>
int main()
{ 
	int i,sum = 0;
	for(i=1;i<=100;i++)
		sum+=i;
	printf("%d\n",sum);
}

2.while 循环

#include<stdio.h>
int main()
{ 
	int i,sum = 0;
	i=1;
	while(i<=100)
	{ 
		sum+=i;
		i++;
	}
	printf("%d\n",sum);
}

3.do-while循环

#include<stdio.h>
int main()
{ 
	int i,sum = 0;
	i=1;
	do
	{ 
		sum+=i;
		i++;
	}
	while(i<=100);
	printf("%d\n",sum);
}