[m0niSx]

well, you better use gets instead of scanf
you can use simply

Код:

float a,b,c,x1,x2,D;  
  gets(a); 
  gets(b);
  gets©;
  printf("readed:\na= %f\nb= %f\nc= %f\n",&a,&b,&c);

and if you still like to use scanf you have to do

Код:

float a,b,c,x1,x2,D;  
  scanf("%f",&a); 
  scanf("%f",&b); 
  scanf("%f",&c); 
  printf("readed:\na= %f\nb= %f\nc= %f\n",&a,&b,&c);

hope that help you