Function pointer

Original - C Code #include <stdio.h> #include <stdbool.h> // get_data(data, prompt, validator): Read data from user and use a custom validator. // The data is verified by calling the specified validator. If the validator returns false, // then the prompt is repeated until the user enters valid data. void get_data(double *data, const char *prompt, bool (*validator)(double)); // Validator functions: these should return true if the value is valid; false otherwise. bool validate_height(double height); bool validate_weight(double weight); bool validate_any(double any) {return true;} // always valid // main: demonstrate use of get_data() with function pointers int main() { double height, weight, random; get_data(&height, "Enter your height in cm: ", validate_height); get_data(&weight, "Enter your weight in kg: ", validate_weight); get_data(&random, "Enter a random number: ", validate_any); printf("\nThanks, here is your info summary:\n" "Height: %.2f cm\n" "Weight: %.2f kg\n" "Random: %g\n", height, weight, random); return 0; } bool validate_height(double height) { if (height < 5.0 || height > 300.0) return false; return true; } bool validate_weight(double weight) { if (weight < 10.0 || weight > 500.0) return false; return true; } void get_data(double *data, const char *prompt, bool (*validator)(double)) { for (;;) { printf("%s", prompt); if (scanf("%lf", data) != 1) { fflush(stdin); // skip over non-numeric data printf("A number is required.\n"); continue; } getchar(); // skip whitespace if ((*validator)(*data)) return; printf("Sorry, that was not a valid number.\n"); } }

#include <stdio.h>
#include <stdbool.h>
 
// get_data(data, prompt, validator): Read data from user and use a custom validator.
// The data is verified by calling the specified validator. If the validator returns false,
// then the prompt is repeated until the user enters valid data.
void get_data(double *data, const char *prompt, bool (*validator)(double));
 
// Validator functions: these should return true if the value is valid; false otherwise.
bool validate_height(double height);
bool validate_weight(double weight);
bool validate_any(double any) {return true;}  // always valid
 
// main: demonstrate use of get_data() with function pointers
int main()
{
    double height, weight, random;
    get_data(&height, "Enter your height in cm: ", validate_height);
    get_data(&weight, "Enter your weight in kg: ", validate_weight);
    get_data(&random, "Enter a random number: ", validate_any);
    
    printf("\nThanks, here is your info summary:\n"
            "Height: %.2f cm\n"
            "Weight: %.2f kg\n"
            "Random: %g\n", 
            height, weight, random);
    return 0;
}
 
bool validate_height(double height)
{
    if (height < 5.0 || height > 300.0)
        return false;
    return true;
}
 
bool validate_weight(double weight)
{
    if (weight < 10.0 || weight > 500.0)
        return false;
    return true;
}
 
void get_data(double *data, const char *prompt, bool (*validator)(double))
{
    for (;;) {
        printf("%s", prompt);
        if (scanf("%lf", data) != 1) {
            fflush(stdin);  // skip over non-numeric data
            printf("A number is required.\n");
            continue;
        }
        getchar();  // skip whitespace
        if ((*validator)(*data))
            return;
        printf("Sorry, that was not a valid number.\n");
    }
} 

double(*trig_fn)(double);
trig_fn = &sin ;
double x = trig_fn( theta ) ;

Original - C Code double (*trig_fn)(double); trig_fn = sin ; double x = (*trig_fn)(theta);

    double (*trig_fn)(double);
    trig_fn = sin ;
    double x = (*trig_fn)(theta);