# C Program to Find Standard Deviation (User Defined Function)

**Question: ** Write a program in C to read an array containing n numbers and find standard deviation using user defined function. Use two different user defined function one for calculating mean and one to calculate standard deviation.

## Standard Deviation Using User Defined Function

```
#include<stdio.h>
#include<math.h>
/* Function prototypes */
float stddev(float a[100], int n);
float mean(float a[100], int n);
void main()
{
float a[100], res;
int i, n;
clrscr();
printf("Enter n:\n");
scanf("%d", &n);
/* Reading array */
for(i=0;i< n;i++)
{
printf("a[%d]=",i);
scanf("%f", &a[i]);
}
/* Function Call */
res = stddev(a,n);
/* Displaying result */
printf("Standard deviation = %f", res);
return 0;
}
/* Function definition for stddev */
float stddev(float a[10], int n)
{
int i;
float fsum=0.0, m;
m = mean(a,n);
for(i=0;i< n;i++)
{
fsum = fsum + (a[i]-m)*(a[i]-m);
}
return(sqrt(fsum/n));
}
/* Function definition for mean */
float mean(float a[10], int n)
{
int i;
float sum=0.0;
for(i=0;i< n;i++)
{
sum = sum + a[i];
}
return(sum/n);
}
```