c - scanf reading more than required -

i coding program in c requires user enter 3 inputs. using scanf numbers:

printf("enter first value: "); scanf("%lf", &eps);  while(eps < 0){     printf("epsilon must positive. choose new value: ");     scanf("%lf", &eps); } printf("enter second value: "); scanf("%lf ", &a); while(a < 0){     printf("a must positive. enter new value: ");     scanf("%lf", &a); }  if (a != 0){     printf("enter third value: ");     scanf("%lf", &w);      while(w < 0){         printf("w must positive. enter new value: ");         scanf("%lf", &w);     } } 

the problem is, when second input required, put value , scanf ignore , "asks new number" (i mean, if enter 1, need enter 1 again value read). haven't been using c while, remember had problem before , used getch() or getchar() after scanf problem didn't happen. doing wrong?

thanks in advance!

there unfortunate space character in scanf format here:

scanf("%lf ", &a); 

that cause scanf swallow whitespace following number, including newline character , whitespace in next line (which means insist on reading line.)

remove space , should work ok.