Why am I getting Segmentation fault. Raspberry pi 4 C Programming - c

Question

#include <linux/module.h>
#include <linux/kernel.h>
//#include <linux/init.h>
#include <linux/types.h>
#include <linux/input.h>
//#include <linux/input-polldev.h>
//#include <linux/delay.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/mman.h>
#include <fcntl.h>
#include <errno.h>
#include <string.h>
#include <unistd.h>
#include <time.h>
#include <stdint.h>
/*
MAHIR SHAHRIAR
30027575
CPSC 359
ASSIGNMENT 2
*/
#define GPIO_CLOCKPIN 23 // pin used for clock output GPIO 11 (SPI_SCLK)
#define GPIO_LATCHPIN 21 // pin used for latch output GPIO 9 (SPI_MISO)
#define GPIO_DATAPIN 19 // pin used for data input from controller GPIO 10 (SPI_MOSI)
#define GPIO_POWERPIN 1 // 3.3 VOLT POWER SOURCE Programmble input to set high/low
#define GPIO_GROUNDPIN 9 // Pin used for grounding
#define GPIO_BASEADDRESS 0xfe200000 // Base address used to offset to other registers
//volatile unsigned *gpio = (unsigned*)0xfe200000; // gpio pointer to base address
volatile uint32_t *gpio = (unsigned*)0xfe200000;
volatile uint32_t *GPFSEL1 = (unsigned*)0xfe200000 + 0x04/4; //pointer to register GPFSEL1 for pins 10-19
volatile unsigned *GPFSEL2 = (unsigned*)0xfe200000 + 0x08/4; //pointer to register GPFSEL2 for pins 20-29
volatile unsigned *GPSET0 = (unsigned*)0xfe200000 + 0x1c/4; //pointer to register GPSET0 for setting high
volatile unsigned *GPCLR0 = (unsigned*)0xfe200000 + 0x28/4; //pointer to register GPCLR0 for setting low
volatile unsigned *GPLEV0 = (unsigned*)0xfe200000 + 0x34/4; //pointer to register GPLEV0 for reading data from pin
volatile unsigned *GPIO_PUP_PDN_CNTRL_REG1 = (unsigned*)0xfe200000 + 0xe8/4; //pointer to register for controlling pull up pull down
// INIT GPIO Function takes user inputs for Initializing a particular GPIO Pin number.
// It takes data such as the PIN NUMBBER , string "input" or "output" ,
// string "high" or "low " and string "pullup" or "pulldown"
// Depending on the arguments passed into the Init_GPIO function or subroutine
static void Init_GPIO(int pin_number, char type, char high_low, char pullup_pulldown) {
// setting valueinput valueoutput and mask to set the input output of the pin type
int valueinput = 0b000 << ( (pin_number-10)*3 ); // bits to be set for input
int valueoutput = 0b001 << ( (pin_number-10)*3 ); // bits to be set for output
int mask = 0b111 << ( (pin_number-10)*3 ); // for ensuring other bits dont change
// condition to check which register to access for the bits and setting to input or output based on
// function calls from main and arguments passed
if(pin_number<=19){
if(type == 'i'){
printf("%x", GPFSEL1);
//*GPFSEL1 = (*GPFSEL1 & ~mask) | (valueinput * mask); //problem
}
else if(type == 'o'){
//*GPFSEL1 = (*GPFSEL1 & ~mask) | (valueoutput * mask);
}
else{
//no type specified
printf("Input type not specified please use 'o' or 'i' ignore if not specifying output input type for pin\n");
}
if(pin_number > 19 && pin_number <=29 ){
if(type == 'i'){
//*GPFSEL2 = (*GPFSEL2 & ~mask) | (valueinput * mask);
}
else if(type == 'o'){
//*GPFSEL2 = (*GPFSEL2 & ~mask) | (valueoutput * mask);
}
else{
//no type specified
printf("Input type not specified please use 'o' or 'i' ignore if not specifying output input type for pin\n");
}
}
// Setting the pin to either high or low
if(high_low == 'h'){
//*GPSET0 = 1 << pin_number;
}
else if(high_low == 'l'){
//*GPCLR0 = 1 << pin_number;
}
else{
// high low not specified
printf("high low not specified please use 'h' or 'l' ignore if not specifying highlow for pin\n");
}
}
// Setting if the pin uses pull up or pull down register
int value_pullup = 0b01 << ( (pin_number -16)*2 );
int value_pulldown = 0b10 << ( (pin_number -16)*2 );
mask = 0b11 << ( (pin_number -16)*2 );
if(pullup_pulldown == 'p'){
//*GPIO_PUP_PDN_CNTRL_REG1 = ( *GPIO_PUP_PDN_CNTRL_REG1 & ~mask ) | (value_pullup) & mask;
}
else if(pullup_pulldown == 'n'){
//*GPIO_PUP_PDN_CNTRL_REG1 = ( *GPIO_PUP_PDN_CNTRL_REG1 & ~mask ) | (value_pulldown) & mask;
}
else {
// user does not set any pull up or pull down value for the assigned pin
printf("pull up pull down not specified please use 'p' or 'n' ignore if not specifying pullup pulldown for pin\n");
}
}
void main() {
printf("pointer address %p " , gpio);
Init_GPIO(18, 'i', 'l', 'p');
volatile uint32_t valueinput = 0b000 << ( (18-10)*3 ); // bits to be set for input
volatile uint32_t valueoutput = 0b001 << ( (18-10)*3 ); // bits to be set for output
volatile uint32_t mask = 0b111 << ( (18-10)*3 );
*GPFSEL1 = (*GPFSEL1 & ~mask) | (valueinput * mask);
}
I am getting segmentation error for the last line in main. I dont know why this is doing that. How do I fix the issue I am trying to change the bits in the register GPFSEL1 for the raspberry pi 4 GPIO for changing the input mode by changing bits to 000 for my pin 18 for putting in into input mode. Any help or direction would be greatly appreciated!