Program to reverse the first n characters in a file in C.

#include <stdio.h>
#include <conio.h>
#include <string.h>
#include <process.h>

void main(int argc, char *argv[])
{
char a[15];
char s[20];
char n;
int k;
int j=0;
int i;
int len;
FILE *fp;

if(argc!=3)
{
puts("Improper number of arguments.");
exit(0);
}
fp = fopen(argv[1],"r");
if(fp == NULL)
{
puts("File cannot be opened.");
exit(0);
}

k=*argv[2]-48;
n = fread(a,1,k,fp);
a[n]='';
len=strlen(a);
for(i=len-1;i>=0;i--)
{
s[j]=a[i];
printf("%c",s[j]);
j=j+1;
}
s[j+1]='';
getch();
}
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