Adding a lot of C code

.gitignore

@@ -32,3 +32,4 @@
 # Debug files
 *.dSYM/
 
+.idea/

env_vars/Makefile

@@ -0,0 +1,7 @@
+P=
+OBJECTS=
+CFLAGS = -g -Wall -O3 
+LDLIBS=
+CC=gcc
+
+$(P): $(OBJECTS)

env_vars/README.md

@@ -0,0 +1,20 @@
+# Environment Variables
+
+Ok this is kind of getting interesting.
+
+## Building
+
+This makefile is kind of interesting. To build and name our program we just need to:
+
+```
+make P="env"
+```
+Ok I don't really know the magic that is going on behind that one. Notice though that you are passing that variable after calling the program.
+Technically, I think it's supposed to work like this:
+
+```
+make CFLAGS="-g -Wall" Set a makefile variable.
+CFLAGS="-g -Wall" make Set an environment variable that only make and its children see.
+```
+
+But on my mac I am noticing only the set makefile variable method works.

env_vars/env.c

@@ -0,0 +1,14 @@
+#include <stdlib.h> //getenv, atoi
+#include <stdio.h> //printf
+
+int main(){
+	// pointer to a char
+	char *repstext=getenv("reps");
+	int reps = repstext ? atoi(repstext) : 10;
+	
+	char *msg = getenv("msg");
+	if (!msg) msg = "Hello.";
+	
+	for (int i=0; i< reps; i++)
+		printf("%s\n", msg);
+}

file_io/Makefile

@@ -0,0 +1,7 @@
+
+
+csv_writer:
+	gcc -o csv_writer csv_writer.c
+
+clean:
+	rm -f csv_writer

file_io/csv_writer.c

@@ -0,0 +1,56 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#define FILE_EXTENSION ".csv"
+
+
+int main(int argc, char const *argv[]){
+
+	if (argc <= 1){
+		fprintf(stderr, "Failed to provide a csv file\n");
+		exit(1);
+	}
+
+	size_t file_len = strlen(argv[1]);
+	
+	/*char pointer of*/
+	char * FILE_NAME = malloc(file_len + 1);
+	if (FILE_NAME == NULL){
+		fprintf(stderr, "Failed to allocate memory for file name!");
+		exit(1);
+	}
+
+	/* Copy file name from executable's first arguments.*/
+	strcpy(FILE_NAME, argv[1]);
+
+	/*Returns a pointer to the location the substring if found*/
+	if (strstr(FILE_NAME, FILE_EXTENSION) == NULL ){
+		fprintf(stderr, "What the fuck are you doing? That %s isn't a csv file!\n", FILE_NAME);
+		free(FILE_NAME);
+		FILE_NAME = 0;
+		exit(1);
+	}
+
+	char name[128], phone_number[13];
+	// puts(FILE_NAME);
+	FILE *_target_file = fopen(FILE_NAME, "a");
+	if (_target_file == NULL){
+		exit(1);
+
+	}
+
+	puts("Name: ");
+	scanf("%s", name);
+	puts("Number: ");
+	scanf("%s", phone_number);
+
+	printf("Appending %s and %s to %s", name, phone_number, FILE_NAME);
+	fprintf(_target_file,"%s,%s\n", name, phone_number);
+	fclose(_target_file);
+	/*clean up*/
+	free(FILE_NAME);
+	FILE_NAME = 0;
+
+	return 0;
+}

file_io/dirp.csv

@@ -0,0 +1 @@
+Margot,517-775-7040

headers/Makefile

@@ -0,0 +1,11 @@
+.PHONY: clean
+P=temp_count
+OBJECTS= temp.o temp_count.o
+CFLAGS = -g -Wall -O3
+LDLIBS=''
+CC=gcc
+
+$(P): $(OBJECTS)
+
+clean:
+	rm -f *.o $(P)

hello/Makefile

@@ -0,0 +1,7 @@
+.PHONY: clean
+
+hello:
+	gcc hello.c -o hello -g -Wall -O3
+
+clean:
+	rm -f *.o hello

pointers/Makefile

@@ -0,0 +1,17 @@
+CFLAGS=-Wall -O3
+PROGRAMS=simple_pointer adv_pointer
+
+all: $(PROGRAMS)
+
+simple_pointer:
+	gcc -o simple_pointer $(CFLAGS) simple_pointer.c
+
+adv_pointer:
+	gcc -o adv_pointer $(CFLAGS) adv_pointer.c
+
+# NOT IMPLEMENTED
+#array_pointer:
+#	gcc -o array_pointer -Wall -O1 array_pointer.c
+
+clean:
+	rm -f $(PROGRAMS)

pointers/README.md

@@ -0,0 +1,5 @@
+#Pointers
+
+Following this [C Pointers Tutorial].
+
+[C Pointers Tutorial]: https://www.cprogramming.com/tutorial/c/lesson6.html

pointers/adv_pointer.c

@@ -0,0 +1,30 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+
+int main(void){
+	int o = 1337;
+
+	printf("Let's learn to use malloc!\n");
+	int *p = malloc(sizeof(*p));
+	/* We need to make sure we got the memory block*/
+	if (p){
+		fprintf(stdout, "Ok we got a good value from malloc we can assign a value.\n");
+	}
+	else {
+		fprintf(stderr, "Well fuck this didn't work. Malloc failed");
+		return 1;
+	}
+
+	printf("Ok the address of o is on the stack at: %p\n", &o);
+	printf("*p is on the heap at: %p\n", p);
+	printf("Let's assign a value to p: \n");
+	scanf("%d", p);
+	printf("We got %d\n", *p);
+
+	printf("Freeing up the memory\nClosing program...\n");
+	free(p);
+	p = 0;
+
+	return 0;
+}

pointers/simple_pointer.c

@@ -0,0 +1,18 @@
+#include <stdio.h>
+
+int main(void){
+
+	int x;
+	int *p;
+
+	/* Read it, "assign the address of x to p" */
+	p = &x;
+	printf("This should be random: %d\n", *p);
+	printf("Ok the address of x is %p\n", &x);
+	printf("Check that p has the same value: %p\n\n", p);	
+
+	printf("Ok let's put a value in the pointer. Give me an int: \n");
+	scanf("%d", p);
+	printf("The value you provided was %d\n", *p);
+	printf("Let's check x since p was a pointer to x's memory address: %d\n", x);
+}

static/Makefile

@@ -0,0 +1,5 @@
+all:
+	gcc -o eggs -Wall -O3 eggs.c
+
+clean:
+	rm -f eggs

structs/Makefile

@@ -0,0 +1,16 @@
+CC=gcc
+CFLAGS=-Wall -O1
+PROGRAMS=pixel struct2
+
+all: $(PROGRAMS) 
+
+pixel:
+	$(CC) -o pixel $(CFLAGS) pixel.c
+
+struct2:
+	$(CC) -o struct2 $(CFLAGS) struct2.c
+
+clean:
+	rm -f $(PROGRAMS)
+
+.PHONY=clean