CS50x: Introduction to Computer Science Programming in C Syllabus

Programming in C syllabus — full chapter and topic list

Expand any chapter to see its topics and sub-topics. This is the whole examinable outline for Programming in C in CS50x: Introduction to Computer Science, not a summary of it.

1. 1

   C Fundamentals

   4 topics

   • Source Code, Machine Code, and Compilers
   • Syntax and Escape Sequences
   • Header Files and Libraries
   • Variables and Constants
2. 2

   Data Types and Operators

   4 topics

   • Data Types
   • Operators
   • Integer Overflow
   • Floating-Point Imprecision
3. 3

   Control Flow

   3 topics

   • Conditional Statements
   • Loops
   • Functions and Pseudocode
4. 4

   Command Line and Development Environment

   3 topics

   • Visual Studio Code and the CLI
   • Linux Commands
   • Manual Pages
5. 5

   Arrays and Strings

   5 topics

   • Compilation Pipeline
   • Arrays
   • Strings as Arrays of Characters
   • Command-Line Arguments
   • Exit Status
6. 6

   Cryptography

   2 topics

   • Encryption and Ciphers
   • Encoding and Decoding

Programming in C flashcards for CS50x: Introduction to Computer Science

24 of 50 cards from the Programming in C deck — real questions with worked answers.

1. What is source code?

   The human-readable set of instructions a programmer writes in a programming language such as C. It must be translated into machine code before a computer can execute it.

2. What is machine code?

   The binary sequence of $0$s and $1$s that a computer's CPU can execute directly. It is the output of compiling source code.

3. What is a compiler?

   A program that translates source code written in a language like C into machine code (binary) that the computer can run. CS50 uses the compiler clang.

4. What command compiles hello.c with clang and names the output program 'hello'?

   clang -o hello hello.c — the -o flag specifies the output file name. Without it, clang produces a default file named a.out.

5. What does the command 'make hello' do in CS50?

   make is a build utility that automatically runs the compiler (clang) with the correct flags on hello.c, producing an executable named hello, so you don't have to type the full clang command yourself.

6. What punctuation must end most statements in C, and what happens if it is missing?

   A semicolon ( ; ). Omitting it is a syntax error, and the compiler will refuse to compile the program until it is fixed.

7. What is an escape sequence in C, and which one prints a new line?

   An escape sequence is a backslash followed by a character that represents a special character in a string. \n moves the cursor to a new line, e.g., printf("hello, world\n");

8. What do the escape sequences \" , \\ , and \0 represent in C?

   \" prints a literal double quote inside a string; \\ prints a literal backslash; \0 is the NUL character (a byte of all zeros) that terminates strings.

9. Which printf format specifiers are used for a string, an int, a float/double, a char, and a long?

   %s for a string, %i (or %d) for an int, %f for a float or double, %c for a char, and %li for a long.

10. What does the line #include <stdio.h> do in a C program?

    It tells the preprocessor to copy the contents of the header file stdio.h (the standard input/output header) into the program, declaring functions like printf so the compiler recognizes them.

11. What is a header file in C?

    A file ending in .h that contains declarations (prototypes) of functions and other symbols provided by a library, e.g., stdio.h declares printf. Including it lets your code call those library functions.

12. What does the CS50 library (cs50.h) provide?

    Convenience functions for safely getting user input — such as get_int, get_float, get_char, get_long, and get_string — plus the string type. Include it with #include <cs50.h>.

13. What is a library in programming?

    A collection of pre-written code (functions) that programmers can reuse in their own programs, accessed in C by including the library's header file and linking its compiled code.

14. How do you declare and initialize an integer variable named counter with value 0 in C, and why must you state the type?

    int counter = 0; C is a statically (strongly) typed language, so every variable must be declared with its data type, which tells the compiler how much memory to allocate and how to interpret it.

15. How do you declare a constant in C, and what naming convention is used?

    Use the const keyword, e.g., const int TOTAL = 10; The value can never be changed afterward, and by convention constant names are written in all uppercase letters.

16. In C, what is the difference between = and == ?

    = is the assignment operator (stores a value in a variable); == is the equality comparison operator (checks whether two values are equal, returning true or false). Using = inside a condition is a classic bug.

17. How many bytes does an int use in C, and what range of values can it store?

    An int uses 4 bytes ($32$ bits) and stores values from $-2^{31}$ to $2^{31}-1$, i.e., roughly $-2{,}147{,}483{,}648$ to $2{,}147{,}483{,}647$.

18. How many bytes does a char use in C, and what does it store?

    A char uses 1 byte ($8$ bits) and stores a single character encoded as a number (its ASCII value), covering $2^{8} = 256$ possible values.

19. Compare float and double in C.

    Both store real (floating-point) numbers. A float uses 4 bytes ($32$ bits); a double uses 8 bytes ($64$ bits), giving roughly twice the precision (more digits after the decimal point). Doubles reduce, but do not eliminate, floating-point imprecision.

20. How many bytes does a long use in C, and why would you use it instead of int?

    A long uses 8 bytes ($64$ bits), storing values from $-2^{63}$ to $2^{63}-1$. Use it when a value might exceed the int maximum of $2^{31}-1$, at the cost of more memory.

21. What is the bool data type in C and what values can it hold?

    A Boolean type holding only true or false. It is not built into old C; it comes from cs50.h (or the standard header stdbool.h).

22. What is the 'string' type used in CS50, and what is it really in standard C?

    string is a type defined by cs50.h for a sequence of characters. Standard C has no string type — it is actually char *, a pointer to an array of characters ending with the NUL byte \0.

23. What does the modulo operator % do in C? Give an example.

    It yields the remainder after integer division. Example: $52 \bmod 10 = 2$, so in C, 52 % 10 evaluates to 2. It is commonly used to check even/odd: n % 2 == 0 means n is even.

24. What are three equivalent ways to increase an int variable counter by 1 in C?

    counter = counter + 1; counter += 1; and counter++; (similarly counter-- decreases it by 1).

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