4 Digit 7 Segment Stopwatch help

I am a beginner with coding, and when I run my code, it only shows 4 zeros. I want an on/off button to go with it, and I am stuck figuring it out. Can someone help me?

Here is my code:
//the pins of 4-digit 7-segment display attach to pin2-13 respectively
int a = 2;
int b = 3;
int c = 4;
int d = 5;
int e = 6;
int f = 7;
int g = 8;
int p = 13;
int d1 = 12;
int d2 = 11;
int d3 = 10;
int d4 = 9;
//int dp=14;
long n = 0;// n represents the value displayed on the LED display. For example, when n=0, 0000 is displayed. The maximum value is 9999.
int x = 100;
int del = 5;//Set del as 5; the value is the degree of fine tuning for the clock
int count = 0;//Set count=0. Here count is a count value that increases by 1 every 0.1 second, which means 1 second is counted when the value is 10
void setup()
{
//set all the pins of the LED display as output
pinMode(d1, OUTPUT);
pinMode(d2, OUTPUT);
pinMode(d3, OUTPUT);
pinMode(d4, OUTPUT);
pinMode(a, OUTPUT);
pinMode(b, OUTPUT);
pinMode(c, OUTPUT);
pinMode(d, OUTPUT);
pinMode(e, OUTPUT);
pinMode(f, OUTPUT);
pinMode(g, OUTPUT);
pinMode(p, OUTPUT);
}
/***************************************/

void loop()
{

clearLEDs();//clear the 7-segment display screen
pickDigit(0);//Light up 7-segment display d1
pickNumber((n / 1000)); // get the value of thousand
delay(del);//delay 5ms

clearLEDs();//clear the 7-segment display screen
pickDigit(1);//Light up 7-segment display d2
pickNumber((n % 1000) / 100); // get the value of hundred
delay(del);//delay 5ms

clearLEDs();//clear the 7-segment display screen
pickDigit(2);//Light up 7-segment display d3
pickNumber(n % 100 / 10); //get the value of ten
delay(del);//delay 5ms

clearLEDs();//clear the 7-segment display screen
pickDigit(3);//Light up 7-segment display d4
pickNumber(n % 10); //Get the value of single digit
delay(del);//delay 5ms

}
/**************************************/
void pickDigit(int x) //light up a 7-segment display
{
//The 7-segment LED display is a common-cathode one. So also use digitalWrite to set d1 as high and the LED will go out
digitalWrite(d4, HIGH);
digitalWrite(d3, HIGH);
digitalWrite(d2, HIGH);
digitalWrite(d1, HIGH);
digitalWrite(p, HIGH);

switch (x)
{
case 0:
digitalWrite(d4, LOW);//Light d1 up
break;
case 1:
digitalWrite(d3, LOW); //Light d2 up
break;
case 2:
digitalWrite(d2, LOW); //Light d3 up
break;
default:
digitalWrite(d1, LOW); //Light d4 up
break;
}
}
//The function is to control the 7-segment LED display to display numbers. Here x is the number to be displayed. It is an integer from 0 to 9
void pickNumber(int x)
{
switch (x)
{
default:
zero();
break;
case 1:
one();
break;
case 2:
two();
break;
case 3:
three();
break;
case 4:
four();
break;
case 5:
five();
break;
case 6:
six();
break;
case 7:
seven();
break;
case 8:
eight();
break;
case 9:
nine();
break;
}
}
void clearLEDs() //clear the 7-segment display screen
{
digitalWrite(a, LOW);
digitalWrite(b, LOW);
digitalWrite(c, LOW);
digitalWrite(d, LOW);
digitalWrite(e, LOW);
digitalWrite(f, LOW);
digitalWrite(g, LOW);
digitalWrite(p, LOW);
}

void zero() //the 7-segment led display 0
{
digitalWrite(a, HIGH);
digitalWrite(b, HIGH);
digitalWrite(c, HIGH);
digitalWrite(d, HIGH);
digitalWrite(e, HIGH);
digitalWrite(f, HIGH);
digitalWrite(g, LOW);
}

void one() //the 7-segment led display 1
{
digitalWrite(a, LOW);
digitalWrite(b, HIGH);
digitalWrite(c, HIGH);
digitalWrite(d, LOW);
digitalWrite(e, LOW);
digitalWrite(f, LOW);
digitalWrite(g, LOW);
}

void two() //the 7-segment led display 2
{
digitalWrite(a, HIGH);
digitalWrite(b, HIGH);
digitalWrite(c, LOW);
digitalWrite(d, HIGH);
digitalWrite(e, HIGH);
digitalWrite(f, LOW);
digitalWrite(g, HIGH);
}
void three() //the 7-segment led display 3
{
digitalWrite(a, HIGH);
digitalWrite(b, HIGH);
digitalWrite(c, HIGH);
digitalWrite(d, HIGH);
digitalWrite(e, LOW);
digitalWrite(f, LOW);
digitalWrite(g, HIGH);
}

void four() //the 7-segment led display 4
{
digitalWrite(a, LOW);
digitalWrite(b, HIGH);
digitalWrite(c, HIGH);
digitalWrite(d, LOW);
digitalWrite(e, LOW);
digitalWrite(f, HIGH);
digitalWrite(g, HIGH);
}

void five() //the 7-segment led display 5
{
digitalWrite(a, HIGH);
digitalWrite(b, LOW);
digitalWrite(c, HIGH);
digitalWrite(d, HIGH);
digitalWrite(e, LOW);
digitalWrite(f, HIGH);
digitalWrite(g, HIGH);
}

void six() //the 7-segment led display 6
{
digitalWrite(a, HIGH);
digitalWrite(b, LOW);
digitalWrite(c, HIGH);
digitalWrite(d, HIGH);
digitalWrite(e, HIGH);
digitalWrite(f, HIGH);
digitalWrite(g, HIGH);
}

void seven() //the 7-segment led display 7
{
digitalWrite(a, HIGH);
digitalWrite(b, HIGH);
digitalWrite(c, HIGH);
digitalWrite(d, LOW);
digitalWrite(e, LOW);
digitalWrite(f, LOW);
digitalWrite(g, LOW);
}

void eight() //the 7-segment led display 8
{
digitalWrite(a, HIGH);
digitalWrite(b, HIGH);
digitalWrite(c, HIGH);
digitalWrite(d, HIGH);
digitalWrite(e, HIGH);
digitalWrite(f, HIGH);
digitalWrite(g, HIGH);
}

void nine() //the 7-segment led display 9
{
digitalWrite(a, HIGH);
digitalWrite(b, HIGH);
digitalWrite(c, HIGH);
digitalWrite(d, HIGH);
digitalWrite(e, LOW);
digitalWrite(f, HIGH);
digitalWrite(g, HIGH);
}
/*******************************************/
void add()
{
// Toggle LED
count ++;
if (count == 10)
{
count = 0;
n++;
if (n == 59)
{
n = 0;
}
}
}

You are making very hard work of driving a 7 segment display. See the last few posts of How do I write this IF statement? - #20 by k1ng_1337 for a better way

Hello,
your sketch would be perfect for usage of struct() to collect all neccessary data in one point for an easy access.
Do you are familar with the usage of struct´s?

No.

@ paulpaulson What do you propose to put in the struct ?

I am not sure. All I want is the stopwatch and an on and off button that controls it. I tried using videos and websites, but it didn’t work for me.

Forget about the struct, at least for now, what experience of programming do you have ?

Very little

Hello
the struct contains the pin number and the logical state of the pin wrt the number to be presented.

This?
int a = 2;
int b = 3;
int c = 4;
int d = 5;
int e = 6;
int f = 7;
int g = 8;
int p = 13;
int d1 = 12;
int d2 = 11;
int d3 = 10;
int d4 = 9;

@ paulpaulson
Sorry, I am still not getting it. Are you perhaps suggesting an array of structs ?

Hello,
yes indeed. This will be an array for the number from ‘0’ to ‘9’ including ‘.’ using defintion given by the struct.

So do you know how to put a button with it?

@ paulpaulson
Sounds OK but I am not sure that @ steve_111 is quite ready for that, but we shall see

My advice would be to get the display showing a running counter first, then worry about stop/start/lap functionality using a button or buttons

So, how do I completely test the code?

From this page:

A switch statement can have an optional default case, which must appear at the end of the switch. The default case can be used for performing a task when none of the cases is true. No break is needed in the default case.

This is why all your digits are showing zero.

If you want help with your current code then please start by Auto formatting your code in the IDE, selecting all of it, using Copy for forum in the IDE and pasting it here so that it is in code tags to make it easier to read and copy for examination

The easier you make it to read and copy the code the more likely it is that you will get help

It says there are no changes necessary for auto format

So how can I fix that?