分支和循环

1.

#include<stdio.h>
int main(void)
{
    double num1,num2;
    char op;

    printf("Type in an expression:");
    scanf("%lf%c%lf",&num1,&op,&num2);

    if(op=='+')
        printf("=%.2f\n",num1+num2);
    else if(op=='-')
        printf("=%.2f\n",num1-num2);
    else if(op=='*')
        printf("=%.2f\n",num1*num2);
    else if(op=='/')
        printf("=%.2f\n",num1/num2);
    else
        printf("Unknown operator\n");

    return 0;

}

2.

#include<stdio.h>
int main(void)
{
    
    double x,y;               
     
    printf("请输入电量:\n");
    scanf("%Lf",&x);
    if(x<0){
           printf("sorry,erro");
        }
        else  if(x<=50){
                y=0.53*x;
        }
        else{
             y=50*0.53+(x-50)*0.58;
        }
            printf("y=%.3f\n",y);
        
        return 0;
     }

3.

#include <stdio.h> 
int main() 
{ 
    double x,pow = 1.0; 
    int i,n; 
   
    printf("Enter x and n：\n"); 
    scanf("%Lf%d",&x,&n);
    
    for(i=1;i<=n;i++)
    pow=pow*x;
    printf("pow(%Lf%d)=%.2f\n",x,n,pow);

    return 0;
}

4.

#include<stdio.h>
int main(void)
{
    int m,n,i;
    double y;    
    y=0;
    printf("Enter m,n：");
    scanf("%d%d",&m,&n);

    for(i=m;i<=n;i++)
       y=y+(i*i+1.0/i);
        
    printf("y=%Lf\n",y);
    
}

5.

#include<stdio.h>
int main(void)
{
    int i,n;
    double item,sum,flag; 
    
    flag =1;    
    sum =0;
    printf("Enter n:");
    scanf("%d",&n);

    for(i=1;i<=n;i++){
        item=(flag*i)/(2*i-1);       
        flag=-flag;
        sum=sum+item;
    }
           printf("sum=%f\n",sum);   
}

6.

#include<stdio.h>
#include<math.h>
int main(void)
{
    int month,year,loan,lower,money,upper;
    double rate;
    lower=5;
    upper=30;
    printf("Enter loan：");
        scanf("%d",&loan);
printf("Enter rate：");
    scanf("%Lf",&rate);
    printf("Enter year：");
    for(year=lower;year<=upper;year++){
        month=year*12;
        money=(loan*rate*pow((1+rate),month))/(pow((1+rate),month)-1);
        printf("%d:  %d\n",year,money);
    }
        return 0;
    }

7.

#include<stdio.h>
#include<math.h>
int main(void)
{
    int n,i;
    double sum,item;
    sum=0;
    printf("Enter n：");
    scanf("%d",&n);

    for(i=1;i<=n;i++){
        item=powl(2,i);
        sum=sum+item;
    }
    printf("sum=%Lf\n",sum);

    return 0;
}