/********************************************************
** Highlight software by yzfy(雨中飞燕) http:// *
*********************************************************/
#include<stdio.h>
double f1(double a,double b,double c)
{
    double a,b,c;
    scanf("%d%d%d",a,b,c);
    printf("x1=-%d+sqrt(%d-%d)\n",b,b*b,4*a*c);
    printf("x2=-%d-sqrt(%d-%d)\n",b,b*b,4*a*c);

}
double f2(double a,double b,double c)
{
    double a,b,c,s;
    scanf("%d%d%d",a,b,c);
    printf("x=-%d-sqrt(%d-%d)\n",b,b*b,4*a*c);
}
double f3(double a,double b,double c)
{
    double a,b,c,s1,s2;
    scanf("%d%d%d",a,b,c);
    printf("x1=-%d+sqrt(%d-%d)*i\n",b,b*b,4*a*c);
    printf("x2=-%d-sqrt(%d-%d)*i\n",b,b*b,4*a*c);
}
main()
{
    double a,b,c,d;
    scanf("%d%d%d",a,b,c);
    d=b*b-4*a*c;
    if(d>0)
        f1(a,b,c);
    else if(d==0)
        f2(a,b,c);
    else(d<0)
        f3(a,b,c);

}
[程序错误很多，由于我不懂函数，自己检查不出错。大家帮帮忙。

[[it] 本帖最后由 bianchengfeng 于 2008-5-12 10:18 编辑 [/it]]

求根公式错了吧。。。。

（-b+sqrt(Δ)）/2*a
（-b-sqrt(Δ)）/2*a
是这样的吧。。。。

呵呵，的确，写忘记了。不过还是有问题啊？

输入的时候，要加地址运算符&

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

double f1(double a,double b,double c);
double f2(double a,double b,double c);
double f3(double a,double b,double c);

double f1(double a,double b,double c)
{
    printf("x1=-%lf+sqrt(%lf-%lf)/2*%lf\n",b,b*b,4*a*c,a);
    printf("x2=-%lf-sqrt(%lf-%lf)/2*%lf\n",b,b*b,4*a*c,a);

}
double f2(double a,double b,double c)
{
    printf("x=-%lf-sqrt(%lf-%lf)/2*%lf\n",b,b*b,4*a*c,a);
}
double f3(double a,double b,double c)
{
    printf("x1=-%lf+sqrt(%lf-%lf)/2*%lf\n",b,b*b,4*a*c,a);
    printf("x2=-%lf-sqrt(%lf-%lf)/2*%lf\n",b,b*b,4*a*c,a);
}
int main(void)
{
    double a,b,c,d;
    scanf("%lf%lf%lf",&a,&b,&c);
    d=b*b-4*a*c;
    if(d>0)
        f1(a,b,c);
    else if(d==0)
        f2(a,b,c);
    else
        f3(a,b,c);
    return 0;
}

语法错误已经修正。至于逻辑的错误，楼主自己修正吧！