wrong result when find the number of digit inside a string - c

Question

Here is the situation:
First, The input consists of the number of test cases, m, in the first line and followed by m test cases. Each test case consists of a string with less than 256 characters. The String may contain "Space bar". My Programming language is C.
Then, here is my problem. I cannot find any problem in my code and I can perfectly run the example with correct result. However, when I upload it onto online judgement system, it shows "WA(Wrong Answer)".
Here is my code.
#include<stdio.h>
int numberOfDigit(char input[255])
{
int num = 0;
for (int i = 0; input[i] != '\0'; i++) {
if (input[i] >= 48 && input[i] <= 57)
num++;
}
return num;
}
int main()
{
int numberOfTestCase;
char input[255];
int digit[9999];
scanf("%d", &numberOfTestCase);
for (int j = 0; j < numberOfTestCase; j++) {
fseek(stdin, 0, SEEK_END);
gets(input);
digit[j] = numberOfDigit(input);
}
for (int k = 0; k < numberOfTestCase; k++) {
printf("%d\n", digit[k]);
}
return 0;
}
I want to explain something in my process of coding.
Because the input contains space character, I use gets() function so that I can get a string without stopping by typing space.
However, if I don't add fseek(stdin, 0, SEEK_END);, gets() only appears numberOfTestCase-1 times, I asked on stackOverflow, and was advised that fseek(stdin, 0, SEEK_END); can solve the problem, which I don't know why. But when I add it, the problem is solved, but it fails tests in the online judgement system.
What is my mistake?

Answer 1

fgets() would stop reading input if it sees a newline. Also fseek() may not work on stdin and it's unnecessary for your purpose. Instead you can fgets() to read the first line too instead of scanf(). And then you can use sscanf() to read the input number.
Something like:
fgets(input, sizeof input, stdin);
sscanf(input, "%d", &numberOfTestCase);
for (int j = 0; j < numberOfTestCase; j++) {
fgets(input, sizeof input, stdin);
digit[j] = numberOfDigit(input);
}
for (int k = 0; k < numberOfTestCase; k++) {
printf("%d\n", digit[k]);
}
You can also use the chracter constants instead of hard-coding ASCII values, which is more readable and portable:
for (int i = 0; input[i] != '\0'; i++) {
if (input[i] >= '0' && input[i] <= '9')
num++;
}