Checking a variable meanwhile calling the functions needed - c

Question

So im fairly new to programming and I ran into something which I cannot figure out.
I'll demonstrate my problem.
int main(void){
int number;
if(number == 1){
number1();
}else if(number == 2){
number2();
}else if(number == 3){
number3();
}else if(number == 4){
number4();
}else if(number == 5){
number5();
}else if(number == 6){
number6();
}else if(number == 7){
number7();
}else if(number == 8){
number8();
}else if(number == 9){
number9();
}else if(number == 0){
number0();
} else if (number >= 10 && <= 19){
number1();
number2(25);
}
}
void number1(int Q){
VGA_box(X + 5 + Q, 20, X+7 + Q, 60, white);
}
void number2(int Q){
VGA_box(X + Q, 20, X+ 20 + Q, 22, white);
VGA_box(X + 18 + Q, 22, X+ 20 + Q, 38, white);
VGA_box(X + Q, 38, X+ 20 + Q, 40, white);
VGA_box(X + Q, 40, X+ 2 + Q, 58, white);
VGA_box(X + Q, 58, X+ 20 + Q, 60, white);
}
Please ignore the functions VGA_box(), since this is just a function to write a line/box.
I'm making a little game and I would like to add a scoreboard, but here is my problem:
Since I'm drawing the numbers (so they look better IMO), I have to call functions, functions which represent a number. So if number = 1, function number1(); is called.
Is there an easy way to call the functions number2(), number5() and number9() if the number is 259? Or lets say; 632. The only possible way I can figure out is to use a lot of if-statements but that will take me a while to do.
Is it possible to use a for-loop which keeps track of what the number is and calls the functions which needed?
Thank you in advance.

Answer 1

You can use an array of pointers to function and a recursive function to reverse the value:
#include <stdio.h>
static void func0(void) { printf("0\n"); }
static void func1(void) { printf("1\n"); }
static void func2(void) { printf("2\n"); }
static void func3(void) { printf("3\n"); }
static void (*func[])(void) = {func0, func1, func2, func3};
static void exec(int value)
{
if (value) {
exec(value / 10);
func[value % 10]();
}
}
int main(void)
{
exec(123);
return 0;
}
Output:
1
2
3
As pointed out by #user3078414 in comments this fails when exec(012) is passed (the first 0 is not evaluated in the recursive function), in addition, 012 is interpreted as an octal (not as a decimal).
An alternative using strings:
#include <stdio.h>
static void func0(void) { printf("0\n"); }
static void func1(void) { printf("1\n"); }
static void func2(void) { printf("2\n"); }
static void func3(void) { printf("3\n"); }
static void (*func[])(void) = {func0, func1, func2, func3};
int main(void)
{
char *ptr = "012";
while (*ptr) {
func[*ptr - '0']();
ptr++;
}
return 0;
}

Answer 2

It seems like functions number1(), number2(), etc are quite similar. I'd be against creating different functions; I'd rather create one single function (let's say number()) which receives the whole number "632" from your example, and loops digit by digit.
Creating one single function is easier to handle by you. Just check that the resulting function is not too big, but it's quite likely that functions number1(), number2(), etc have a lot of code in common. If that's the case, reducing redundancy and repetition in code is highly recommended!
Let me know if I'm right with this.
Cheers!

Answer 3

Create function drawDigit(int digit) where digit is a single digit number between 0 and 9.
You can use function pointers to select which number function to call, but if that is too complex, you can use the if/else method for now.
Convert score to string:
int score = 259;
char digits[SIZE]; // Size must be large enough to hold all digits and nul character ('\0')
int numDigits = snprintf(digits, SIZE, "%d", score); // snprintf is from "stdio.h"
// digits contains now 4 character string "259" with nul character at the end
Loop over string to draw all digits:
for(int i = 0; i < numDigits; ++i) {
int digit = digits[i] - '0'; // Convert character digit to numeric digit
drawDigit(digit);
}
You probably need extra a parameter to drawDigit function to adjust the horizontal placement, but I'll leave that exercise to the reader.

Answer 4

Function pointers and switch/case are not the solution !
The problem is not if-statement or even the functions. Since your algorithms to draw scores are very different in each function then you can not stop using lots of conditions, so you have to some where call them by lots of if statements.
The solution is to find an uniform algorithm to draw scores on the screen for every number. For example write 10 functions to draw digits between [0..9], then use this functions to draw numbers with arbitrary length numbers.

Answer 5

You can use pointer to function, e.g:
#include <stdio.h>
typedef void (*typ_callback)(int);
static void number1(int Q);
static void number2(int Q);
typ_callback my_table[] = { NULL, number1, number2 };
int main(void)
{
size_t number;
printf("Entern the number of callback: ");
scanf("%zu", &number);
if (number <= (sizeof(my_table)/sizeof(my_table[0])))
{
if (my_table[number] != NULL)
{
my_table[number](number);
}
}
else
{
fprintf(stderr, "Wrong number\n");
}
return 0;
}
static void number1(int Q)
{
printf("You called %s function with passing value %d\n", __func__, Q);
}
static void number2(int Q)
{
printf("You called %s function with passing value %d\n", __func__, Q);
}