>>307
#include <stdio.h>

int main(void)
{
FILE *in, *out;
char buff[256];
int i;

if((in=fopen("in.txt", "r"))==NULL) return 0;
if((out=fopen("out.txt", "w"))==NULL) return 0;

for(i=0; fgets(buff, sizeof buff, in); i++) fprintf(out, "%04d:%s", i, buff);

fclose(in);
fclose(out);

return 0;
}