Convert to all upper case letter bug in C

I'm a noob so please explain why the following code isn't working? It prints an unnecessary Case 1:. I assume it's not scanning using fgets the first time in the Test Case loop.

Please someone tell me why.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main() {
    int i, j, T;
    scanf("%d", &T); //test cases
    char character[100];
    for (j = 1; j <= T; j++) {
        fgets(character, 100, stdin); //input
        for (i = 0; i <= strlen(character); i++) { //function
            if (character[i] >= 91) {
                character[i] = character[i] - 32;
            };
        }
        printf("Case %d: %s", j, character); //result
    }
    return 0;
}

Solution

There are multiple issues in your code:

you should read the pending newline after getting the number with scanf().
you do not check for end of file
you include the null terminator in the loop, a simpler test is this:
```
  for (i = 0; character[i] != '\0'; i++)
```
you should use <ctype.h> to convert lower case to upper case or at least use character constants instead of hardcoded ASCII values. The current code would also convert such characters as {, |, }... because they happen to be >= 91.
91 is incorrect anyway. 'a' has value 97 in ASCII.

Here is a modified version:

#include <ctype.h>
#include <stdio.h>

int main() {
    int i, j, T;

    if (scanf("%d", &T)) != 1) //test cases
        return 1;
    getchar();  // read pending newline
    char character[100];
    for (j = 0; j < T; j++) {
        if (!fgets(character, sizeof character, stdin)) //input
            break;
        for (i = 0; character[i] != '\0'; i++) { //function
            character[i] = toupper((unsigned char)character[i]);
        }
        printf("Case %d: %s", j + 1, character); //result
    }
    return 0;
}

ASCII specific version:

#include <stdio.h>

int main() {
    int i, j, T;

    if (scanf("%d", &T)) != 1) //test cases
        return 1;
    getchar();  // read pending newline
    char character[100];
    for (j = 0; j < T; j++) {
        if (!fgets(character, sizeof character, stdin)) //input
            break;
        for (i = 0; character[i] != '\0'; i++) { //function
            if (character[i] >= 'a' && character[i] <= 'z') {
                character[i] -= 'a' - 'A';
            }
        }
        printf("Case %d: %s", j + 1, character); //result
    }
    return 0;
}