to upper case every words in file in C - c

Question

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);
}

Answer 1

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.

Answer 2

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#define MAX 20
char *mygets(char *s, size_t sz) {
int ch;
size_t i = 0;
while((ch = getchar()) != '\n' && i < sz)
s[i++] = ch;
s[i] = '\0';
return s;
}
int main(void) {
FILE *fPtr;
char filename[MAX+1];
int c, i;
printf("Enter name of file: ");
mygets(filename, MAX+1);
if(!strstr(filename, ".txt"))
strcat(filename, ".txt");
if((fPtr = fopen(filename, "r+")) == NULL) {
fprintf(stderr, "Could not open %s\n", filename);
exit(1);
}
i = 0;
while((c = fgetc(fPtr)) != EOF) {
fseek(fPtr, i, SEEK_SET);
fputc(toupper(c), fPtr);
i++;
}
rewind(fPtr);
while((c = fgetc(fPtr)) != EOF)
putchar(c);
fclose(fPtr);
return 0;
}