Note "passing functions as paramters"

Pointer to function

A pointer to a function is an ordinary type in the C-language. It can be declared as, for example, the following,

double (*f)(double);

Now f is a variable containing a pointer to a function that takes one double argument and returns a double result.

One can assign a value to this variable and then use it as a normal function, for example, after #include"math.h",

f=sin;
printf( "%g\n", f(1) );

Functions as arguments

One can pass (pointers to) functions as arguments to other functions just like any other variables, for example,

#include"stdio.h"
#include"math.h"

void print_f_of_1 ( double (*f)(double) ) {
        printf("f_of_1=%g\n",f(1));
        }

int main(){
        print_f_of_1 (sin);
        print_f_of_1 (cos);
        print_f_of_1 (tan);
return 0;
}

Pointers to functions in arrays and structures

Pointers to functions, like other types of variables, can be elements of arrays, for example,

#include"stdio.h"
#include"math.h"

int main(){
        double (*f[3])(double) = {sin,cos,tan};
        for(int i=0;i<3;i++)printf("%g\n",f[i](1));
return 0;
}

or members of structures, for example,

#include"stdio.h"
#include"math.h"
struct funs {double (*a) (double); double (*b) (double);};
int main(){
        struct funs F = {.a=sin,.b=cos};
        printf("%g %g\n",F.a(1),F.b(1));
return 0;
}