实验3

#include<stdio.h>
#include<math.h>
int main()
{
    float a,b,c,x1,x2;
    float delta,real,imag;
    printf("Enter a, b, c: ");
    while( scanf("%f%f%f",&a,&b,&c) != EOF)
    {
        if( a==0 )            printf("not quadratic equation.\n\n");
        else
        {
            delta = b*b-4*a*c;
            if( delta>=0 )
            {
                x1 = ( -b+sqrt(delta))/(2*a);
                x2 = ( -b-sqrt(delta))/(2*a);
                printf("x1 = %.2f, x2 = %.2f\n\n", x1, x2);
            }
            else
            {
            real = -b/(2*a);
            imag = sqrt(-delta)/(2*a);
            printf("x1 = %.2f + %.2fi, x2 = %.2f - %.2fi\n\n", real,imag,real,imag);
            }
        }
        printf("Enter a, b, c: ");
    }
    return 0;
 }

#include<stdio.h>
#include<stdlib.h>
#include<time.h>
#define N 5
int main()
{
    int x,n;
    srand(time(0));
    n=0;
    do
    {
        n++;
        x = rand()%10;
        printf("%34d",x);
    } while( n<N );
    printf("\n");
    return 0;
 } 

#include<stdio.h>
#include<math.h>
int isprime( int );
int main()
{
    int a,b;
    scanf("%d %d",&a,&b);
    int i;
    int sum=0;
    for( i=a;i<=b;i++)
    {
        if( isprime( i ) )
        {
            printf("%5d",i);
            sum++;
        }
    }
    printf("\n");
    printf("%d~%d之间共有%d个素数",a,b,sum);
    return 0;
 } 
 
 
 
 int isprime( int n )
 {
     int i;
     int flag=1;
     for( i=2;i<sqrt(n);i++)
     {
         if( n%i==0)
         {
             flag=0;
             break;
         }
     }
     if( flag==0)    return 0;
     else return 1;
 }

#include<stdio.h>
int main()
{
    long s;
    printf("Enter a number: ");
    while( scanf("%ld",&s) != EOF)
    {
        int a[100];
        int i=0;
        while( s>0 )
        {
            if( s%10 != 0 && (s%10)%2!=0 )
            {
                a[i]=s%10;
                i++;
             } 
             s /= 10;
        }
        printf("new number is: ");
        for( i;i>=0;i--)
        {
            if( a[i]!=0)
            printf("%d",a[i]); 
        }
        printf("\n");
        printf("Enter a number: ");
    }
    return 0;
}

#include<stdio.h>
int fac( int );
int main()
{
    int n;
    printf("Enter n(1~10):  ");
    while( scanf("%d",&n )!= EOF )
    {
        double sum=1.0;
        if( n==1 )
        {
            printf("1\n");
            break;
        }
        else
        {
            int i;
            for( i=2;i<=n;i++)
            {
                if( i%2==0 )
                {
                    sum-=(double)(1.0/fac(i));
                }
                else
                {
                    sum+=(double)(1.0/fac(i));
                }
            }
        }
        printf("n=%d, s=%f",n,(double)sum);
        printf("\n");
        printf("Enter n(1~10):  ");
    }
}



int fac( int n )
{
    int i;
    int sum=1;
    for( i=1;i<=n;i++)
    {
        sum*=i;
    }
    return sum;
}