Need help calculating standard deviation

#include <iostream>
#include<cmath>
#include <complex>

using namespace std;

void input(double &grade1, double &grade2, double &grade3);
void calc(int &while1, double &grade1, double &grade2, double &grade3, double &min, double &max, double &avg, double &dev);
void repeat(int &while1);

int main() {

	double min, max, avg, dev, grade1, grade2, grade3;
	int def = 1;
	int while1;
	do {
		switch(def) {
		case 1:
		input(grade1, grade2, grade3);
		calc(while1, grade1, grade2, grade3, min, max, avg, dev);
		break;
		default:

			break;
		}
	} while(while1 == 1);

	return 0;
}

void input(double &grade1, double &grade2, double &grade3) {
	cout << "Enter the three test scores for the student, separated by a space: " << endl;
	cin >> grade1;
	cin >> grade2;
	cin >> grade3;
}

void calc(int &while1, double &grade1, double &grade2, double &grade3, double &min, double &max, double &avg, double &dev){
	double avg1;

	if ((grade1 > grade2) && (grade1 > grade3)) {
			max = grade1;
	} else if (grade2 > grade3) {
		max = grade2;
	} else if (grade3 > grade2) {
		max = grade3;
	}

	if ((grade1 < grade2) && (grade1 < grade3)) {
		min = grade1;
	} else if ((grade2 < grade1) && (grade2 < grade3)) {
		min = grade2;
	} else if ((grade3 < grade2) && (grade3 < grade1)) {
		min = grade3;
	}

	avg = grade1+grade2+grade3;
	avg1 = avg/3;
	cout << "AVG Output: " << avg1 << endl;


	cout << "The student's statistics are: " << endl;
	cout << "Minimum = " << min << " Maximum = " << max << " Average = " << avg1 << " Standard Deviation = " << endl;
	repeat(while1);
	}

void repeat(int &while1) {
	char t;
	cout << "Do you want to calculate the statistics for another student? (y/n): " << endl;
	cin >> t;
	if (t == 'y') {
		while1 = 1;
	} else if (t == 'n') {
		while1 = 0;
	}
}