Triangular number

# include<stdio.h>
void triangular(long);
int main()
{
long N;
scanf("%ld",&N);
triangular(N);
return 0;
}
void triangular(long N)
{
long i,total=0;
for(i=1;i<=N;i++)
total=total+i;
printf("%d",total);
}

Finding Fibonacci number

# include<stdio.h>
void fibonacci(long);
int main()
{
long N;
scanf("%ld",&N);
fibonacci(N);
return 0;
}
void fibonacci(long N)
{
long i,f0=0,f1=1,f;
for(i=1;i<=N;i++)
{
f=f0+f1;
f1=f0;
f0=f;
printf("%3d",f);
}
}

Finding Prime number

# include<stdio.h>
# include<math.h>
long prime(long);
int main()
{
long N,i;
scanf("%ld",&N);
if(prime(N)!=0&&prime(N)!=1)
printf("%ld is a prime number",N);
else
printf("%ld is not a prime number",N);
return 0;
}

long prime(long N)
{
long j;
for(j=2;j<=(int)sqrt(N);j++)
if(N%j==0)
return 0;
return N;
}