How do I print Invalid for letters - c

Question

How do I print invalid when someone enter big or small letters, because supposedly they only enter floats between 0 to 10.
I tried coding like this
It went so wrong.
#include<stdio.h>
int main()
{
int trial=0;
float judge1=0,judge2,judge3,judge4,judge5;
char a;
printf("\n%90s","Welcome to the constentant score calculator program :)");
printf("\n\n\n\n\n\rKindly enter the constentant score by 5 respected
judges:");
do
{
printf("\n\nScore by JUDGE 1 (0-10):\t");
scanf("%f",&judge1);
if ((judge1>-1)&& (judge1<11) )
printf("The constentant got %.2f from the judge",judge1);
else
printf("\aPlease input a valid score between 0 and 10:");
} while ((judge1<0) || (judge1>10)||(judge1=a>96) && (judge1=a<123)||
(judge1=a<91) && (judge1=a>64));
}
okay this is my second code
#include<stdio.h>
int main()
{
float judge1;
printf("\n%90s","Welcome to the constentant score calculator program :)");
printf("\n\n\n\n\n\rKindly enter the constentant score by 5 respected
judges:");
printf("\n\nScore by JUDGE 1 (0-10):\t");
scanf("%f",&judge1);
if ((judge1>-1) && (judge1<11))
printf("The constentant got %.2f from the judge",judge1);
else
printf("\aPlease input a valid score between 0 and 10:");
}
}

Answer 1

When you use the "%f" as the format string for scanf, it will read only characters that are valid for a floating point type and will stop reading if it detects any other characters. So if someone types "abc", nothing is written to judge1 and those characters are left in the input buffer to be read again. You'll then get stuck in an infinite loop reading those same characters.
Also, this expression doesn't make sense:
judge1=a>96
> has higher precedence than ==, so it is equivalent to:
judge1=(a>96)
Assuming a is assigned a value, a>96 compares that value with 96 and evaluates to either 0 or 1. Then you assign this value to judge1, overwriting what was read from the user. Assuming you meant to use == this doesn't make sense either. That being the case, either judge1==0 or judge1==1 is evaluated depending on the result of a>96. So the above expression will only be true if judge1 is 1 and a is greater than 96 or judge1 is 0 and a is less than or equal to 96.
Another problem is that a is never assigned a value. You seem to be under the impression that when you call scanf("%f",&judge1); that the first character read is written to a. There is no link that causes that to happen, so a is left uninitialized.
What you want to do instead is read in a line of text using fgets, then using strtof to read a float. The strtof function accepts the address of a pointer as the second parameter to let you know where in the string the parsing stopped. So if this pointer does not point to the null terminator at the end of the string (or to a newline character, since fgets reads and stores the newline), then you know you read a non-float character.
float judge1;
char line[100];
char *p;
int invalid_input;
do {
invalid_input = 0;
fgets(line, sizeof(line), stdin);
errno = 0;
judge1 = strtof(line, &p);
if (errno || ((*p != 0) && (*p != '\n')) || (judge1 < 0) || (judge1 > 10)) {
printf("Please input a valid score between 0 and 10:");
invalid_input = 1;
} else {
printf("The constentant got %.2f from the judge\n ",judge1);
}
} while (invalid_input);

Answer 2

First, check the return value of scanf. If it fails to match the item it will return 0. Then you can check whether the number entered is within bounds:
int r, judge1;
...
r = scanf("%d", &judge1);
if(r != 1)
{
printf("invalid input\n");
while((r = fgetc(stdin)) != EOF && r != '\n');
}
else if((judge1 < 0) || (judge1 > 10))
printf("input out of range\n");
else
printf("valid input\n");

Answer 3

The problem is you have the bad charachter stuck in the stream. The solution is here:
scanf fails why?.
The suggested thing to do from John Bode is to use a getchar to get it out. Also apply the check mnistic suggested and it should work.
it doesn't offer anything and it only messes with the greater picture.