Text file with C in terminal - c

Question

So I calculated the mean and standard deviation from double values read within a file.
My file data has 1 number per line:
My data in the file is the following
1
2
3
4
5
6
7
8
9
10
My code is below:
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
int main(){
FILE *inputfile;
char name[100];
printf("Enter the file you want to use to calculate standard deviation:\n ");
gets(name);
inputfile = fopen(name, "r");
if (inputfile == NULL)
{
printf("Failed to open text file.\n");
exit(1);
}
double i;
double j=1;
double average;
double stdish=0;
double stdreal=0;
double x=0;
double sum=0;
double stdfinal;
while(fscanf(inputfile, "%lf", &i) != EOF){
x=x+1;
sum = sum + i;
j =pow(i,2);
stdreal +=j;
}
average = sum/x;
stdish = (stdreal/x)-(pow(average,2));
stdfinal = sqrt(stdish);
printf("The average is %.4lf\n", average);
printf("The standard deviation is %.4lf\n", stdfinal);
return 0;
}
My standard deviation is incorrect, and I am not sure why.
In my program, I use fopen to get the text from the input file.
Also, I am trying to make it so that I input the text file from the terminal instead of in the actual program itself. How to do that?

Answer 1

First you need to find out the average (mean) and then iterate through the loop to find out the variance. The SQRT(variance) will give you standard deviation.
double CalculateMean()
{
double sum = 0;
for(int i = 0; i < max; i++)
sum += value[i];
return (sum / max);
}
double CalculateVariane()
{
mean = CalculateMean();
double temp = 0;
for(int i = 0; i < max; i++)
{
temp += (value[i] - mean) * (value[i] - mean) ;
}
return temp / max;
}
Reference: http://www.softwareandfinance.com/CPP/MeanVarianceStdDevi.html

Answer 2

Declare main as int main(int argc, char *argv[]) or as int main(int argc, char **argv). They mean the same thing. In this version, argc is the number of command line arguments (+1 because the program name is argument 0). argv is an array of char *s, each of which is a command line argument.
You can do something like this:
int main(int argc, char *argv[])
{
FILE *inputfile;
char name[100];
if(argc == 1) {
printf("Enter the file you want to use to calculate standard deviation:\n ");
gets(name);
} else {
strcpy(name, argv[1]);
}
inputfile = fopen(name, "r");
if (inputfile == NULL)
{
printf("Failed to open text file.\n");
exit(1);
}
double i;
double j=1;
double average;
double stdish=0;
double stdreal=0;
double x=0;
double sum=0;
double stdfinal;
while(fscanf(inputfile, "%lf", &i) != EOF){
x=x+1;
sum = sum + i;
j =pow(i,2);
stdreal +=j;
}
average = sum/x;
stdish = (stdreal/x)-(pow(average,2));
stdfinal = sqrt(stdish);
printf("The average is %.4lf\n", average);
printf("The standard deviation is %.4lf\n", stdfinal);
return 0;
}