求解二次方程ax^2+bx+c=0.应用求根公式：(-b加减 根号b^2-4ac )/2a

#include #include void main(){float equal(float,float);float lessthan(float,float,float);float morethan(float,float,float);float a,b,c,z;printf("ax^2+bx+c=0 \nplease input a,b,c\n");scanf("%f,%f,%f",&a,&b,&c);if(a==0) //判断是否是一元二次方程{ printf("error!"); printf("ax^2+bx+c=0\nplease input a,b,c\n");scanf("%f,%f,%f",&a,&b,&c);}z = b*b-4*a*c;if(fabs(z)0)morethan(a,b,z);if(z