Storing files from keyboard input strings

Write a program: Enter a string from the keyboard, convert all lowercase letters to uppercase letters, and save the output to the disk file "Upper.txt". Enter the string to "! End The contents of the file Upper.txt are then read out and displayed on the screen.

#include <stdio.h>
#include <iostream>
void main()
{
char rev;
FILE *fp;
if((fp=fopen("l:\\upper.txt","a+"))==NULL)
{
　printf("cannot openfile\n");
　exit(0);
}
rev=getchar();
while(rev!='!')
{
　if(rev>='a'&&rev<='z')rev=rev-32;
　fwrite(&rev,sizeof(char),1,fp);
　rev=getchar();
}
rewind(fp);
while(!feof(fp)) putchar(getc(fp));
printf("\n");
fclose(fp);
}