No input detection

[oboy]

I am writing a program to find roots of a cubic function, however, I am getting my inputs from a separate text file. So, there might be a case where I get something like this:
1 2 3 4
5 6 7 8
9 0 1

There might not be enough variables (which I need 4 of) in order to run the program, so scanf is stuck in an infinite loop waiting for an input. Is there something that can detect this problem. So far I have this worked out, but it doesn't work:
insert

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
int main()
{
    double a, b, c, d, f, x=50.0;
    printf("enter:");
    scanf("%lf", &d);
    if(isspace(d))
        printf("No input.");
    return 0;

}

[oboy]

I have tried this too, but no luck:

double a, b, c, d, f, x=50.0;
    printf("enter:");
    int ret1=scanf("%lf", &a);
    int ret2=scanf("%lf", &b);
    int ret3=scanf("%lf", &c);
    int ret4=scanf("%lf", &d);
    if(ret1||ret2||ret3||ret4==0)
        printf("No input.");

It seems like I need a dynamic input tester of some sort. Because it scans for the first value, for the second value, for the third, and so on, but if I press enter, there is nothing happening.

[rags_to_riches]

Cprogramming.com FAQ > How do I get a number from the user (C)

[CommonTater]

I am writing a program to find roots of a cubic function, however, I am getting my inputs from a separate text file. So, there might be a case where I get something like this:
1 2 3 4
5 6 7 8
9 0 1

There might not be enough variables (which I need 4 of) in order to run the program, so scanf is stuck in an infinite loop waiting for an input. Is there something that can detect this problem. So far I have this worked out, but it doesn't work:
insert

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
int main()
{
    double a, b, c, d, f, x=50.0;
    printf("enter:");
    scanf("%lf", &d);
    if(isspace(d))
        printf("No input.");
    return 0;

}

You may want to experiment with this....

#include <stdio.h>
int main (void)
  { double input[4];
     int incount = 0;
 
    while ( incount < 4)
      { rprintf ("Enter value #%d :",incount); 
        if (scanf("%lf", input[incount]) > 0)
          incount++; 
        printf "\n"); }

     return 0; }

To see how this works, check out the return value from scanf() in your documentation...