Hi!!

I need a little help with my program.

I have done a program that calculates mean, variance and standard devisation now I need to add the calculation for confidence interval.

The confidence interval is calculated using this equation:

mean +/- z*(standard deviation/number of samples)

I have added this to my code:

Function prototype: **double conf_int(double n[ ], double stv, double z);**

and

** double z;**

printf ("Enter the z value");

scanf ("%d", &z);

This is wher I get stuck.

I am nto sure on how to do write the code for calculationg confidence interval.

The output for example should look like this: 73.125 +/- 69.536

This is my code

Code:

#include <stdio.h>
#include <math.h>
#define N 12
/* Function prototypes */
double mean(double n[ ]);
double variance(double n[ ], double m);
double std_dev(double v);
double conf_int(double n[ ], double stv, double z);
void main(void)
{
double mu, v, stv;
double num[N] = {87.8, 45.7, 56.7, 78.6, 49.7, 91.2, 87.6, 63.6, 59.8, 98.3, 77.2, 81.3};
double z;
printf ("Enter the z value");
scanf ("%d", &z);
/* int ctr;
for (ctr=0; ctr<N; ctr++)
{
printf ("Please enter the next number . . . ");
scanf ("%f", &num[ctr]);
}
printf ("fdls %f", num[1]); */
mu = mean (num);
v = variance (num, mu);
stv = std_dev(v);
printf ("Mean = %.3f, Variance = %.3f\n", mu, v);
printf ("Standard Deviation = %.3f\n", stv);
printf ("Confidence Interval = %.3f\n", conf_int);
}
double mean(double n[N])
{
double sum=0.0, retVal;
int i;
for (i=0; i<N; i++)
{
sum += n[i];
}
retVal = sum/N;
return retVal;
}
double variance(double n[N], double m)
{
double ctr=0.0, retVal;
int i;
for (i=0; i<N; i++)
{
ctr += pow ((n[i] - m), 2);
}
retVal = ctr/(N-1);
return retVal;
}
double std_dev(double v)
{
double retVal;
retVal = sqrt(v);
return retVal;
}
double conf_int(double n[ ], double stv, double z);
{
?????????????????????????????

**THANK YOU**