main.c

#include "mymath.h"
#include <stdio.h>

int main(){
	double t=5;
	double *p;
	double m;
	p=&t;
	m=square_to(p);
	printf("%f\n%f\n", t, m);
	return 0;
}

mymath.c

#include "mymath.h"
#include <stdio.h>

/* Betrag function */
double aabs(double x){
	if(x<0) return -x;
	else return x;
}

/* Cosinus function */
double cos(double x){
	int i;
	i=1;
	double sum;
	sum=1;
	double summand;
	summand=1;
	double y;
	y=1;
	double z;
	z=1;
	int t;
		
	while(aabs(summand)>0.00001){
		y=y*x*x;
		z=z*(2*i-1)*(2*i);
		if(i%2==0) t=1;
		else t=-1;
		summand=t*y/z;
		sum+=summand;
		i++;
	}
	return sum;
}

/* signum function */
int sgn(double x){
	if(x<0) return -1;
	else return (x!=0);
}

/* square root function */
double sqroot(double a){
	if(a<=0)return 0;
	int i;
	int b;
	b=a;
	for(i=0;i<100000;i++){
		a=0.5*(a+b/a);
	}
	return a;
}

/* prim test */
int prim(int c){
	int n;
	n=2;
	int p=1;
	while(n*n<c){
		if(c%n==0) p=0;
		n++;
	}
	return p;
}

/* größter gemeinsamer Teiler */
int ggt(int a, int b){
	if(a==0) {
		return b;
	}
	while(b!=0){
		if(a>b){
			a=a-b;
		}
		else{
			b=b-a;
		}
	}
	return a;
}

/* e function */
double expo(double x){;
	double summand=1;
	double sum=0;
	int i;
	for(i=1;summand>0.000000001;i++){
		sum+=summand;
		summand*=x/i;
	}
	return sum;
}

/* natural log */
double ln(double x){
	double summand=(x-1)/(x+1);
	double sum=0;
	int i;
	for(i=1;summand>0.000000001;i++){
		sum+=summand;
		summand*=((x-1)/(x+1))*((x-1)/(x+1))*(1./(2*i+1))*(2*i-1);
	}
	return 2*sum;
}

/* power function with e function and ln */
double power(double x, double y){
	return expo(y*ln(x));
}

/* naiv power function */
double power_naiv(double x, int y){
	int i;
	double p=1;
	for(i=0;i<y;i++){
		p*=x;
	}
	return p;
}

/* double and add power function */
double power_dadd(double x, int n){
	if(n==0) return 1;
	double t=1;
	int i;
	for(i=n;i>0;i--){
		if(n%2){
			t=t*x;
			x=x*x;
			i=(i-1)/2;
		}
		else{
			x=x*x;
			i=i/2;
		}
	}
	return t;
}

/* faculty function */
int fac(int x){
	if(x==0) return 1;
	else return x*fac(x-1);
}

/* kth-root of a */
double kroot(double a, int k){
	return power(a, 1./k);
}

/* log x to base a */
double loga(int a, double x){
	return (ln(x)/ln(a));
}

/* return 3rd side with 2 given sides and their angle in a triangle */
double triangle(double a, double b, double w){
	return sqroot(a*a+b*b+2*a*b*cos(w));
}

/* abc formula function */
double abcformel(double a, double b, double c){
	if(a!=0){
		double x;
		double y;
		if(b!=0){
			x=0;
			y=0;
			x=-(b/a)/2+sqroot((b/a)*(b/a)/4-c/a);
			y=-(b/a)/2-sqroot((b/a)*(b/a)/4-c/a);
		}
		else {
			x=sqroot(-c/a);
			y=-sqroot(-c/a);
		}
		if(x>y) return x;
		else return y;
	}
	else return 0;
}

/* Riemann Zeta function */
double zeta(double s){
	double i=0;
	double sum=0;
	double summand=1;
	for(i=1;summand>0.00000001 && summand<10000;i++){
		summand=1/power(i, s);
		sum+=summand;
	}
	return sum;
}

/* größtes Element in Array */
double arrayMax(int *a, unsigned l){
	unsigned i;
	double max=0;
	for(i=0;i<l;i++){
		if(a[i]>max) max=a[i];
	}
	return max;
}

/* Array Gleichheit Test */
int arrayGTest(int *a, int *b, unsigned l){
	unsigned i;
	for(i=0;i<l;i++){
		if(a[i]!=b[i]) return 0;
	}
	return 1;
}

/* vertausche jedes b in a mit c */
void arraybc(int *a, int b, int c, unsigned l){
	unsigned i;
	for(i=0;i<l; i++){
		if(a[i]==b) a[i]=c;
	}
}

/* sort array from smallest to biggest */
void sortArray(int *a, unsigned l){
	unsigned i;
	unsigned k;
	int t;
	for(i=0;i<l;i++){
		for(k=0;k<l-1;k++){
			if(a[k]>a[k+1]) {
				t=a[k];
				a[k]=a[k+1];
				a[k+1]=t;
			}
		}
	}
}

/* prints array */
void printArray(double *a, unsigned l){
	unsigned i;
	for(i=0;i<l;i++){
		printf("%f \n", a[i]);
	}
}

/* abc formula function */
int abcformel2(double a, double b, double c, double l[2]){
	double x;
	double y;
	if(a>0 && b>0 && c>0) return 0;
	if(a==0){
		l[0]=-c/b;
		return 1;
	}
		if(b!=0){
			x=0;
			y=0;
			x=-(b/a)/2+sqroot((b/a)*(b/a)/4-c/a);
			y=-(b/a)/2-sqroot((b/a)*(b/a)/4-c/a);
		}
		else {
			x=sqroot(-c/a);
			y=-sqroot(-c/a);
		}
	l[0]=x;
	l[1]=y;
	return 2;
}

double square_to(double *p){
		*p=(*p)*(*p);
		return *p;
}

mymath.h

#ifndef MYMATH_H
#define MYMATH_H
double aabs(double x);
double cos(double x);
int sgn(double x);
double sqroot(double a);
int prim(int c);
int ggt(int a, int b);
double expo(double x);
double ln(double x);
double power(double x, double y);
double power_naiv(double x, int y);
double power_dadd(double x, int n);
int fac(int x);
double kroot(double a, int k);
double loga(int a, double x);
double triangle(double a, double b, double w);
double abcformel(double a, double b, double c);
double zeta(double s);
double arrayMax(int *a, unsigned l);
int arrayGTest(int *a, int *b, unsigned l);
void arrayab(int *a, int b, int c, unsigned l);
void sortArray(int *a, unsigned l);
void printArray(double *a, unsigned l);
int abcformel2(double a, double b, double c, double l[2]);
double square_to(double *p);

#endif