Converstion to lower to upper case problem

[orangeboy443]

Hey, I'm using C language and I want to tell you my code for a function that needs to convert lowercase to uppercase:

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

void convertL(FILE *fileName)
{
    ClearScreen();
    char name[15];
	char *p;
	printf("\nOption #3\n\n");
	fflush(stdin);
	printf("Enter a file name:  ");
    fgets(name, sizeof(name), stdin);
    fileName = fopen("text.dat", "w");
    if (fileName == NULL) {
        printf("There is an error opening the file.\n");
        exit(1);
    }
    
    char line [MAX_LINE];
    printf("Please enter a line of text:, max %d characters\n", sizeof(line));
    if (fgets(line, sizeof(line), stdin) != NULL) {
       fprintf(fileName, "%s\n", line);
       }
 
     char *o;
   
     printf ("Before conversion: %s\n", line);

     for (o = line; *o != '\0'; ++o)
     {
       *o = toupper(*o);
       ++o;
        }

     printf ("After conversion: %s\n", line);

     
     return;   

}

My output:

Option #1

Enter a file name: name
Please enter a line of text:, max 80 characters
hello there
Before conversion: hello there

After conversion: HeLlO ThErE

Why isnt it making the whole entire text uppercase? It seems like it is skipping characters. What should I change/modify in my code to make it all uppercase??

Thanks

Orange