第三，四章

# include<stdio.h>
int main(void)
{
 
   printf("Progmming is fun.
");
    printf("And programming in C is even more fun!
");


    return 0;
}

#include<stdio.h>
int main(void)
{
    int celsius,fahr;

    fahr=100;
    celsius = 5 * (fahr-32)/9;

    printf("fahr=%d,celsius = %d
",fahr,celsius);

    return 0;
    
}

#include <stdio.h>
int main(void)
{
    double x,y;

    printf("Enterx(x>=0;
");
    
	scanf("%if",&x);
	if(x<=15){
        y=4*x/3;
    }
	else {
		y=2.5*x-10.5; 
	}
	printf("y=f(%f)=%.2f
",x,y);

   return 0;
}

 

#include<stdio.h>
#include<math.h>

int main(void)
{
	int money,year;
	double rate,sum;

	 printf("Enter money:");
          scanf("%d",&money);
	printf("Enter year:");
	scanf("%d",&year);
	printf("Enter rate:");
	scanf("%if",&rate);
	sum=money * pow(1+rate,year);
	printf("sum=%.2f
",sum);

	return 0;
}

 

  

#include<stdio.h>
int main(void)
{
 int fahr,lower,upper;
 double celsius;

 printf("Enter lowor:");
 scanf("%d",&lower);
    printf("Enter upper:");
 scanf("%d",&upper);
 printf("fahr  celsius
");

 
  for(fahr=lower;fahr<=upper;fahr++){
   celsius=(5.0/9.0)*(fahr-32);
   printf("5d%6.1f
",fahr,celsius);
        }

#include<stdio.h>
int main(void)
{
    int i,n,sum;

    printf("Enter n:");
    scanf("%d",&n);
    sum=0;
    for(i=1;i<=n;i++){
        sum=sum+i;
    }
    printf("Sum of numbers from 1 to %d is %d
",n,sum);

    return 0;
}

#include<stdio.h>
int main(void)
{
    int denominator,flag,i,n;
    double item,sum;

    printf("Enter n:");
    scanf("%d",&n);
    flag=1;
    denominator=1;
    sum=0;
    for(i=1;i<=n;i++){
        item=flag*1.0/denominator;
        sum=sum+item;
        flag=-flag;
        denominator=denominator+2;
    }
    printf("sum=%f
",sum);

    return 0;
}

 

#include<stdio.h>
int main(void)
{
    int i,n;
    double product;

    printf("Enter n:");
    scanf("%d",&n);
    product=1;
    for(i=1;i<=n;i++){
        product=product*i;
    }
    printf("product=%.0f
",product);

    return 0;

}