to upper case every words in file in C

can you tell me what adjustments i can do for my code, or any simplifications? What shouldn't i repeat, what should i change ? This code converts every word to upper case, if you find some problems,pls write in order to fix it))

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
int main(){
    FILE * fPtr, *fPtr1;
    int c; /*to store characters*/
    char filename[20];
    char filename2[20] = "temp.txt";
    printf("Enter name of file: ");
    scanf("%19s%*c",filename);
    fPtr = fopen(filename, "r");
    fPtr1 = fopen(filename2, "w");
    c = fgetc(fPtr);
    while(c!=EOF){
        if(c!='\n'){
            if(islower(c)){
                fputc(c-32,fPtr1);
            }else{
                fputc(c,fPtr1);
            }
        }else{
            fputc(c,fPtr1);
        }
        c = fgetc(fPtr);
    }
    fclose(fPtr);
    fclose(fPtr1);
    remove(filename);
    rename(filename2,filename);
    fPtr = fopen(filename, "r");
    c = fgetc(fPtr);
    while(c!=EOF){
        printf("%c",c);
        c = fgetc(fPtr);
    }
    fclose(fPtr);
}

This program does what you say it does. But I recommend some changes that your future self will appreciate.

First, always initialize your variables; this habit will help to prevent odd bugs in your future code. Set ints to a value out of your expected range (e.g. maybe -1 in this case); set pointers to NULL; set char arrays to { '\0' } or to "\0".

Next, check your file pointers (fPtr, fPtr1) for NULL after fopen.

Finally, specific to this code, your check for new-line is unnecessary; islower will return 0 if the parameter is not a lowercase alphabetic character.