Prog#207: read from keyboard until $ & write into file

/*
read from keyboard until $ & write into file
Program#207
*/
#include<stdio.h>
main(int argc,char *argv[])
{
union xyz{
struct bio{
char name [25];
int age;
float salary;
char addr [25];
}a;
char b[sizeof(struct bio)];
};
union xyz m;
FILE *fp;
int i;
if(argc!=2)
{
printf("error. no.of arg");
return 0;
}
fp=fopen (argv[i], "w");
if(fp==NULL)
{
printf("file open error");
return 0;
}
scanf("%s", m.a.name);
while(m.a.name[0]!='$')
{
scanf("%d %f %s", & m.a.age, & m.a.salary, m.a.addr);
for(i=0;i<sizeof(struct bio);i++)
putc(m.b[i],fp);
scanf("%s", m.a.name);
}
fclose(fp);
}