freeCodeCamp.org, 2018 ▶ C Programming Tutorial for Beginners

today i decided to start relearning programming in the C programming language. the reason i decided to learn C is that i feel like i can get a greater understanding of how computers work and be more prepared for [Programming in Rust].

I have been using nix dev/shell environments to manage dependencies lately.

Command	Use
nix-shell shell.nix	Start the nix dev enviroment
gcc -o HelloWorld Hello.c	Compile Hello.c into an executable file named HelloWorld
./HelloWorld	Execute the HelloWorld program

I will be following along with a FreeCodeCamp.org Video on C For more C Programming checkout WIP - “C Programming Full Course for free” by Bro code

Todo

• i skipped the madlibs project cause i have done all the things required for it and dont think it will teach me anything and i wasnt feeling interested in completing it.

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FAQ

Here’s the sections with simple info i always forget.

Logical operators - in C

Sign	Example	Description
>		“Greater-than” sign
<		“Less than” sign
>=		“Greater than or equal to” sign
⇐		”Less than or equal to” sign
=		set equal to
==		compare if equal
&&		And
||		Or
!		Not
!($)		Negation opperator

Variable types

Name’s	Declare	Printf	Scanf
Integer, Whole Number, int	int yourAge = 26;	%d	%d
Float, Decimal Number, double	double gpa = 2.75;	%f	%lf
Character, char	char grade = 'A';	%c	%c
String, char[]	char name[] = "Dani";	%s	%s
Pointer, memory address	char * pGrade = &grade;	%p
File	FILE * fileName = fopen("file.txt", "w");

File functions

• Read
• Write
• Append

Math functions

Function name	Description
sqrt(16)	Square root
ceil(1.4)	Round to ceiling
floor(1.4)	Round to floor
pow(4, 3)	returns the value of x to the power of y

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Hello world - in C

#include <stdio.h>
#include <stdlib.h>
 
int main() {
	printf("Hello world!\n");
	return 0;
	}

#include <stdio.h> is saying include the standard input/output package #include <stdlib.h> is saying include the standard library

int main() {} every C program starts with a “main” function which starts when executed printf(""); This is a standard library function to “print formatted” return 0; each program gives a status code when it exits, status code 0 is like all is well.

Timestamp= 00:09:04

Drawing ASCII shape - in C

#include <stdio.h>
#include <stdlib.h>
 
int main() {
	printf("   /|\n");
	printf("  / |\n");
	printf(" /  |\n");
	printf("/___|\n");
 
	return 0;
	}

pretty self explanatory, just using the printf function to print out an ASCII triangle

Timestamp= 00:12:51

Variables - in C

#include <stdio.h>
#include <stdlib.h>
 
int main() {
	char yourName[] = "Dani";
	int yourAge = 26;
	printf("Hello %s! \n", yourName);
	printf("You are %d years old. \n", yourAge);
 
	yourAge = 15;
	printf("Now your name is %s. \n", yourName);
	printf("and your age is %d. \n", yourAge);
 
	return 0;
	}

%s tells it to insert a string there, it gets the data from the yourName variable.

Data types - in C

#include <stdio.h>
#include <stdlib.h>
  
int main() {
	int yourAge = 26;         // %d
	char yourGrade = 'A';     // %c
	double pi = 3.14;         // %f
	char yourName[] = "Dani"; // %s
	  
	printf("Hello %s! \n", yourName);
	printf("You are %d years old. \n", yourAge);
	printf("The value of Pi is: %f. \n", pi);
	printf("and your grade is %c. \n", yourGrade);
	
	return 0;
}

• Int
• Double
• Char
  • Char array (String)

Working with numbers - in C

#include <stdio.h>
#include <stdlib.h>
  
int main() {
 
	// Square root
	printf("%f", sqrt(16));
 
	// Rounding to floor/ceiling
	printf("%f", ceil(1.4));  
	printf("%f", floor(1.4));
 
	// Power of
	printf("%f", pow(4, 3));
	
	return 0;
}

• Math done with 2 integers will return an integer even if it “should” return a decimal
  • Eg. 5 / 4 = 1 instead of 1.25
• math done with any floats will return a float
  • Eg. 1.25 + 1 = 2.25

Constants - in C

#include <stdio.h>
#include <stdlib.h>
  
int main() {
	// This code will refuse to compile due to trying to rewrite a read only variable
 
	// Set the vars (able to change)
	int yourAge = 26;         // %d
	char yourGrade = 'A';     // %c
	double pi = 3.14;         // %f
	char yourName[] = "Dani"; // %s
 
	// Set the constant vars (Unable to change)
	const int constAge = 26;         // %d
	const char constGrade = 'A';     // %c
	const double constPi = 3.14;     // %f
	const char constName[] = "Dani"; // %s
 
	// Print the vars
	printf("Hello %s! \n", yourName);
	printf("You are %d years old. \n", yourAge);
	printf("The value of Pi is: %f. \n", pi);
	printf("and your grade is %c. \n", yourGrade);
 
	// Print the const vars
	printf("Hello %s! \n", constName);
	printf("You are %d years old. \n", constAge);
	printf("The value of Pi is: %f. \n", constPi);
	printf("and your grade is %c. \n", constGrade);
 
	// Modify the vars
	yourAge = 62;         // %d
	yourGrade = 'F';      // %c
	pi = 3.2;            // %f
	yourName = "Not Dani";    // %s
 
	// Try to modify the constant vars
	constAge = 46;         // %d
	constGrade = 'B';      // %c
	constPi = 3.9;        // %f
	constName = "Also not Dani";    // %s
 
	// Print the vars agian
	printf("Hello %s! \n", yourName);
	printf("You are %d years old. \n", yourAge);
	printf("The value of Pi is: %f. \n", pi);
	printf("and your grade is %c. \n", yourGrade);
 
	// Print the const vars again
	printf("Hello %s! \n", constName);
	printf("You are %d years old. \n", constAge);
	printf("The value of Pi is: %f. \n", constPi);
	printf("and your grade is %c. \n", constGrade);
	
	return 0;
}

• Code like shown above Refuses to compile since you cant rewrite a const
• constants are good for certain known constants like the speed of light, pi, etc.
• Const vars are commonly written in ALL CAPS

Getting user input - in C

#include <stdio.h>
#include <stdlib.h>
  
int main() {
	int age; // printf: %d | scanf: %d
	char grade; // printf: %c | scanf: %c
	double gpa; // printf: %f | scanf: %lf
	char name[20]; // printf: %s | scanf: %s
	
	// you have to specify how many chars to allocate memory for with strings
	// gotta use a pointer to reference the memory address
	
	printf("Enter your name: ");
	fgets(name, 20, stdin);
	// scanf("%s", name); // strings dont need pointers in scanf... Why?
	printf("you entered: %s \n", name);
	
	printf("Enter your grade: ");
	scanf("%c", &grade);
	printf("you entered: %c \n", grade);
	  
	printf("Enter your age: ");
	scanf("%d", &age);
	printf("you entered: %d \n", age);
	  
	printf("Enter gpa: ");
	scanf("%lf", &gpa); // floats are called %lf in scanf... Why?
	printf("you entered: %f \n", gpa);
	  
	return 0;
}

• scanf function works similar to to the printf function but in reverse
• fgets is like scanf but you can include spaces but cant use it for floats, ints, etc
• fgets enter key will insert a new line and then end entry so your var will include a new line character
• %lf instead of %f inside of the scanf function
• you need to use a pointer to reference the memory address but not for strings
• i was getting this warning for the above code: warning: ignoring return value of ‘scanf’ declared with attribute ‘warn_unused_result’

⭐ MadLibs - in C

this is a pretty simple project recreating a madlib using C using the techniques we have already covered. i plan to do it later as its kinda uninteresting to me currently.

Arrays - in C

#include <stdio.h>
#include <stdlib.h>
  
int main() {
	int someNums[] = {1, 2, 4, 8, 16, 32, 64, 128};
	char name[] = "Dani";
	int search;
	printf("choose an index: ");
	scanf("%d", &search);
	printf("index number %d holds the following data: %d \n", search, someNums[search]);
	printf("The first letter of your name is: %c", name[0]); // Strings are just arrays!
	  
	return 0;
}

• Learning about arrays explains a bit more why strings are kinda funky sometimes. strings are just arrays of the char type so you have to treat them as such.
• arrays are kinda fun! remind me of things like CSV files, and working with databases in php/mysql

Functions - in C

#include <stdio.h>
#include <stdlib.h>
 
int main() {
    helloWorld();
    helloUser("Dani", 26);
 
    return 0;
}
 
void helloWorld() {
    printf("Hello world! \n");
}
 
void helloUser(char userName[], int userAge) {
    printf("Hello %s! you are %d years old.", userName, userAge);
}

Super excited to work on some functions in C! unlocking new parts of the superpower!

• works basically how i thought it would.
• not exciting by itself obviously but the possibilities are exciting.

Function return statements - in C

#include <stdio.h>
#include <stdlib.h>
 
double cube(double num) {
	return num * num * num;
}
 
int main() {
    double myNum = 7.0;
    printf("%f cubed is: %f", myNum, cube(myNum));
    return 0;
}

• the return type goes right before the function name
• don’t forget to add a return statement to the function!
• seems like the return type of the main function is int,i wonder if its just convention or makes an actual difference.

If statements - in C

#include <stdio.h>
#include <stdlib.h>
 
int max(int num1, int num2) {
    int result;
    if (num1 > num2) {
        result = num1;
    }
    else {
        result = num2;
    }
    return result;
}
 
int main() {
    int num1 = 8;
    int num2 = 9;
    printf("the bigger number is: %d", max(num1, num2));
}

• i have heard that for most use cases a switch statement is better performing/faster?

Else if statements

#include <stdio.h>
#include <stdlib.h>
 
int maxOf3(int num1, int num2, int num3) {
    int result;
    if (num1 >= num2 && num1 >= num3) {
        result = num1;
    }
    else if (num2 >= num1 && num2 >= num3) {
        result = num2;
    }
    else {
        result = num3;
    }
    return result;
}
 
int main() {
    printf("The max number is: %d", maxOf3(2, 4, 8));
}

• why is a switch statement faster/better?

Switch statements - in C

#include <stdio.h>
#include <stdlib.h>
 
int main () {
    char grade = 'A';
 
    switch (grade) {
        case 'A':
            printf("Great job!");
            break;
        case 'B':
            printf("Good job!");
            break;
        case 'C':
            printf("Good job.");
            break;
        case 'D':
            printf("seems like we need to work on this more.");
            break;
        case 'F':
            printf("See me after class please.");
            break;
        default:
            printf("Invalid grade!");
    }
}

in the case where grade is equal to A print “Great job!”

Structs - in C

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
 
struct User {
    char name[50];
    int age;
    double rating;
};
 
int main() {
    struct User bobby;
    strcpy(bobby.name, "Robert");
    bobby.age = 23;
    bobby.rating = 2.5;
 
    printf("Username: bobby \n
			Name: %s \n
			Age: %d \n
			Rating: %lf", bobby.name, bobby.age, bobby.rating);
    return 0;
}

structs seem pretty useful.

While loops

#include <stdio.h>
#include <stdlib.h>
 
int main() {
    // While loop example
    int index = 11;
 
	printf("Index is starting at: %d \n", index);
 
    while (index <= 10) {
        printf("Index is: %d\n", index);
        index++; // same as putting index = index + 1;
    }
 
	printf("Index is ending at: %d \n", index);
 
    printf("Done!");
 
    return 0;
}

• checks if the condition is true and if its true it executes the code then checks the condition again
• executes code While condition is true
• a while loop doesnt need to keep track of iterations

Do-while loops

#include <stdio.h>
#include <stdlib.h>
 
int main() {
    // While loop example
    int index = 11;
 
	printf("Index is starting at: %d \n", index);
 
    do {
        printf("Index is: %d\n", index);
        index++; // same as putting index = index + 1;
    } while (index <= 10);
 
	printf("Index is ending at: %d \n", index);
 
    printf("Done!");
 
    return 0;
}

• similar to a while loop but it excecutes the code first before checking the condition.
• if the condition is false to start with, it will still execute the code 1 time to start before finally checking if the condition is true and executes code if condition is true(?)

⭐ Guessing game

#include <stdlib.h>
#include <stdio.h>
 
// Goal: create a game to guess the number until user gets it right or runs out of guesses
 
int main() {
    int secret = 7;
    int maxNum = 10;
    int minNum = 1;
    int guessLimit = 3;
    int guess;
    int index = 1;
 
    while (secret != guess && guessLimit >= index) {
        printf("Guess %d/%d | Guess a number between 1 and 10: ", index, guessLimit);
        scanf("%d", &guess);
        if (guess < minNum || guess > maxNum) {
            printf("Reminder that the secret number is between 1 and 10. \n");
        }
        if (guess == secret) {
            printf("Congrats! you got it right on attempt #%d with %d attempts remaining! \n", index, (guessLimit - index));
            break;
        }
        if (secret != guess && guessLimit <= index) {
            printf("Sorry, you reached your guess limit! (Guess limit: %d) \n", guessLimit);
            break;
        }
        else {
	        // seems like this code would benifit from being a switch statement.
            index++;
        }
    }
}

• take input
• while loop
• if/else
• etc
• proud of the end result
  • i had cleaner looking code earlier but kept changing stuff.

For loops - in C

int i;
int binaryCounting[] = {1, 2, 4, 8, 16, 32, 64, 128}
for (i = 1; i <= 5; i++) {
	// Do something until test condition is met
}
for (i = 0; i <= 8; i++) {
	printf("Position %d: %d \n", i, binaryCounting[i]);
}

• similar idea to while loops but more explicit on incrementing an index

for loop has 3 sections plus the code its executing:

1. the initialization
2. the test condition (a Boolean expression)
3. the update statement
   1. this can be any statement like i--, i = i + 2, a=4, etc
4. code to execute each loop.

2D arrays - in C

#include <stdlib.h>
#include <stdio.h>
 
int main() {
    int nums[3][5] = {
        {1, 2, 3, 4, 5},
        {2, 4, 6, 8, 10},
        {3, 6, 9, 12, 15}
    }
    printf("%d", nums[2][4]); // This will print out the number 15
}

• Arrays where each item is an array
• is an array of strings actually a 2D array since strings are array of characters?

Nested For loops - in C

#include <stdlib.h>
#include <stdio.h>
 
int main() {
    // 2D Array:
    int nums[3][5] = {
        {1, 2, 3, 4, 5},
        {2, 4, 6, 8, 10},
        {3, 6, 9, 12, 15}
    };
    int x;
    int y;
 
    // printf("%d", nums[2][4]); // This will print out the number 15
 
    // Nested for loop:
    for(x = 0; x < 3; x++) {
        printf("\nArray %d: ", x);
        for(y = 0; y < 5; y++) {
            printf("%d ", nums[x][y]);
        };
    };
}

Output:

 
Array 0: 1 2 3 4 5 
Array 1: 2 4 6 8 10 
Array 2: 3 6 9 12 15

• really good for accessing data in a 2D array
• maybe game loops? like the game delta progressing and then if you start taking damage lower health x amount of times? idk

Memory addresses - in C

#include <stdlib.h>
#include <stdio.h>
 
int main() {
    int age = 26;
    double gpa = 3.5;
    char grade = 'A';
 
    printf("Memory address of... \nAge: %p \ngpa: %p \nGrade: %p \n", &age, &gpa, &grade);
    
    return 0; 
}

• Memory addresses are the part of C that intimidates me and i worry i wont be able to understand. we shall see…
• not sure when i would need to use memory addresses but here is how to access them.

Pointers - in C

#include <stdlib.h>
#include <stdio.h>
 
int main() {
    int age = 26;
    int * pAge = &age;
 
    double gpa = 3.5;
    double * pGpa = &gpa;
 
    char grade = 'A';
    char * pGrade = &grade;
 
    printf("Memory address of... \nAge: %p \ngpa: %p \nGrade: %p \n", &age, &gpa, &grade);
    printf("Memory address of... \nAge: %p \ngpa: %p \nGrade: %p \n", pAge, pGpa, pGrade);
    
    return 0; 
}

• pointers are just a memory address
• use & before the name of the variable to address the variables memory address

De-Referencing Pointers - in C

#include <stdlib.h>
#include <stdio.h>
 
int main() {
    int age = 26;
    int * pAge = &age;
 
    double gpa = 3.5;
    double * pGpa = &gpa;
 
    char grade = 'A';
    char * pGrade = &grade;
 
    printf("Memory address using &age \nAge: %p \ngpa: %p \nGrade: %p \n", &age, &gpa, &grade);
    printf("\nMemory address using pAge (pAge = &age) \nAge: %p \ngpa: %p \nGrade: %p \n", pAge, pGpa, pGrade);
 
    printf("---\n");
 
    printf("\nDe-Referenced pointers using *&age \nAge: %d \ngpa: %f \nGrade: %c \n", *&age, *&gpa, *&grade);
    printf("\nDe-Referenced pointers using *pAge \nAge: %d \ngpa: %f \nGrade: %c \n", *pAge, *pGpa, *pGrade);
 
    printf("---\n");
 
    printf("\nMemory address using &*&age \nAge: %p \ngpa: %p \nGrade: %p \n", &*&age, &*&gpa, &*&grade);
    printf("\nMemory address using &*pAge (pAge = &age) \nAge: %p \ngpa: %p \nGrade: %p \n", &*pAge, &*pGpa, &*pGrade);
    
    return 0; 
}

• Basically just fetching the data that is in the memory address?
• when you de-reference a pointer you have to use the * symbol to de-reference it.
• you have to use the datatype stored in the memory address

1. store an int: int age = 26;
2. Reference a pointer: int * pAge = &age;
3. de-reference a pointer: printf("%d", *pAge);
4. re-reference a pointer: printf("%p", &*pAge);

Writing Files - in C

//