Change text file case and copy data in C - c

Question

I am creating a program which copies text file data from one file and changes its case to lower or upper on choice, but when I execute the program I receive the following result and the text case is not changed or copied.
#include <stdio.h>
int main() {
FILE *fp = NULL;
FILE *fp2 = NULL;
char str[200];
char var;
int i;
char copy;
fp = fopen("file1.txt", "a");
fp2 = fopen("file2.txt", "w");
printf("Enter choice: ");
scanf(" %c", &var);
if (fp != NULL && var == 'L') {
while ( fgets(str, 200, fp) != NULL ) {
putchar(tolower(fp[i]));
i++;
}
puts(str);
}
else if (fp != NULL && var == 'U') {
while ( fgets(str, 200, fp) != NULL ) {
putchar(toupper(fp[i]));
i++;
}
puts(str);
}
else {
printf("ERROR: No proper choice was made \n");
}
while (1) {
copy = fgetc(fp);
if (copy == EOF) {
break;
}
else {
putc(copy , fp2);
}
}
return 0;
fclose(fp);
fclose(fp2);
}
The output I get is:
Enter choice: U
▒▒

Answer 1

putchar(tolower(fp[i])); should have generated compiler warnings. Insure the compiler warning are all enabled or consider a new compiler.
Replace in 2 places, both upper and lower section.
while ( fgets(str, 200, fp) != NULL ) {
putchar(tolower(fp[i]));
i++;
}
// With to iterate over each character
while (fgets(str, sizeof str, fp) != NULL) {
for (i=0; str[i]; i++) {
putchar(tolower(str[i]));
}
}
Change to int to properly distinguish all characters returned from fgetc() from EOF.
Open with "r" to read from the beginning of the file
// fp = fopen("file1.txt", "a")
fp = fopen("file1.txt", "r");

Answer 2

The problem is that you use fgets, which reads a string from the file. A better way of doing this would be to use fgetc, which reads just one character at a time and process it appropiately.