For loop and While loop to select values in C - c

Question

Could someone help me to look at the code I wrote in C? It can generate numbers, but the if condition looks like wrong, but I donot know how to fix it.
I need to get some n random values with distribution and these values are in a special intervals, so I use for loop like below:
n=10; mu=2; mu_plus=3; p=0.2;
for(i=1; i<=n; i++)
{
x1 = gasdev(&idum);
x2 = gasdev(&idum);
z = sqrt(1-p*p)*x1 + p*x2 + mu;
z_p= x2 + mu_plus;
if (z > 2.17 || z<-2.17)
{
Z[i]=z;
Z_plus[count]=z_p;
}
printf("%d %lf %lf\n", i, Z[i], Z_plus[i]);
}
Where gasdev() is a function for generating random value with a standard normal distribution, Z and Z_plus are 1*n vectors. The results are mess, so I think that the IF condition must be wrong. Could any one could help me? Thank you.
I also tried the While loop.
while(count < n)
{
x1 = gasdev(&idum);
x2 = gasdev(&idum);
z = sqrt(1-p*p)*x1 + p*x2 + mu;
z_p= x2 + mu_plus;
if (z > 2.17 || z<-2.17)
{
count++;
Z[count]=z;
Z_plus[count]=z_p;
}
printf("%d %lf\n",count, Z[count]);
if (count >n) break;
}
It can print out normally, but occurs an error at the end.
Thank you!

Answer 1

The error here is that you always increment i as part of the for loop so that if z is outside the range of the bracket set, you do not put any value into the Z array. You do not specify count so was that supposed to be i or not?
n=10; mu=2; mu_plus=3; p=0.2;
for(i=1; i<=n; i++)
{
x1 = gasdev(&idum);
x2 = gasdev(&idum);
z = sqrt(1-p*p)*x1 + p*x2 + mu;
z_p= x2 + mu_plus;
if (z > 2.17 || z<-2.17)
{
Z[i]=z;
Z_plus[count]=z_p; // Should this be Z_plus[i] ??
}
// Note that if outside of bracket no value put in Z[i]
// This makes Z[i] and Z_plus[i] garbage
printf("%d %lf %lf\n", i, Z[i], Z_plus[i]);
}
Your while loop is not correct either as it increments count when it is n-1 and tries to process Z[n] when it appears that you must have defined it as an array of size n (max index is n-1). Also the print needs to be inside the if not outside.
while(count < n)
{
x1 = gasdev(&idum);
x2 = gasdev(&idum);
z = sqrt(1-p*p)*x1 + p*x2 + mu;
z_p= x2 + mu_plus;
if (z > 2.17 || z<-2.17)
{
// This allows count == n which overflows the buffer.
count++;
Z[count]=z;
Z_plus[count]=z_p;
}
// This should be inside the bracket not outside
printf("%d %lf\n",count, Z[count]);
// This is not needed since it will exit the while at count == n
if (count >n) break;
}
correct code would be
count = 0;
while(count < n)
{
x1 = gasdev(&idum);
x2 = gasdev(&idum);
z = sqrt(1-p*p)*x1 + p*x2 + mu;
z_p= x2 + mu_plus;
if (z > 2.17 || z<-2.17)
{
Z[count]=z;
Z_plus[count]=z_p;
printf("%d %lf\n",count, Z[count]);
count++;
}
}