急！~请教C语言题目！~谢谢

急！~请教C语言题目！~谢谢

1.float fun (int m)
{
int j,s;
long int k;
float sum;
sum=0;
s=1;
k=1;
for(j=1;j<=m;j++){
sum=sum+(float)s/k;
s=s*(-1);
k=k*(j+1);
}
return sum;
}
main()
{
int n;
scanf( "%d",&n);
printf("%f",fun(n));
}

2.int fun (int year)
{
if( (year%4==0 && year%100!=0) || year%400==0)
return(1);
else
return(0);
}
void main(void)
{
int year ;
printf("please enter year:");
scanf("%d",&year);
if(fun(year)) printf("bissextile");
else printf("not bissextile");
}

3.# include

int invert(long m)
{
printf("%ld",m%10);
m=m/10;
if(m==0)
return 1;
invert(m);
}

void main(void)
{
long n;
printf("Enter n:");
scanf("%ld",&n);
invert(n);
printf("\n");
}

郁闷麽