C语言规律循环累加求和案例

#include <stdio.h> 
void main(){
 
	int i;
	float a,b,c,d,t;
	a = 1.0; b = 2.0; i = 1; t = 0;
	for (i = 1; i <= 20; i++) {
		if (i < 2){
			c = b / a;
			t = c+t;
			a = a + 1; b = b + 1; //第一项不符合规律
			}
		else
		{
			c = b / a;
			t = t + c;
			d = a; a = b; b = d + b;//赋值关系不要搞混
		}	
	}
	printf("2/1+3/2+5/3+8/5.....前二十项和为%f\n",t);
	getchar(); getchar();
}

#include <stdio.h> 
void main(){ 
 
 int i; 
 float a,b,c,d,t; 
 a = 1; b = 2; i = 1; t = 0; 
 for (i = 1; i <= 20; i++) { 
  c = b / a; 
   t = c+t; 
 d = a; a = b; b = d + b; 
} 
printf("2/1+3/2+5/3+8/5.....前二十项和为%.2f\n",t);
}

int factorial(int n)
{ 
 if(n == 0 || n == 1) return 1; // 0和1的阶乘都是1
 return n*(factorial(n-1)); 
}

#include <stdio.h>
int main() {
 double sum = 0;
 double x = 1;
 for(int i = 1; i <= 20; i++) {
  x = x * i;
  sum = sum + x;
 } 
 printf("%f\n", sum); 
}