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); /* f is a pointer to double function of double argument */

The variable f contains 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) );

Interestingly, in the C-language the following phenomena are observed:

One can call both functions and function pointers,

double x = sin(1.0);
double y = (&sin)(1.0); /* apparently allowed */

Ordinary functions are implicitly converted to function pointers (pointing to themselves);

Therefore, the following is equally valid,

double (*f)(double);
f=sin;                   /* sin is implicitly converted to &sin */
printf( "%g\n", f(1) );  /* ok to call function pointer */

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)); /* ok to call function pointer */
        }

int main(){
        print_f_of_1 (&sin);
        print_f_of_1 (&cos);
        print_f_of_1 (tan); /* ok: function is implicitly converted to function pointer */
return 0;
}

Pointers to functions in arrays and structures

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

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

int main(){
        double (*f[3])(double) = {sin,cos,tan};
	f[2]=exp;
        for(int i=0;i<3;i++)printf("%g\n",f[i](1));
return 0;
}

or members of structures,

#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;
}