CS50 Lecture Notes - Week 1: Introduction to C

Overview

• Introduction to C, an older and traditional programming language.
• Concepts from Scratch (week 0) will be revisited: functions, loops, conditionals.
• Focus on problem-solving and expanding toolkits with C programming.
• Discuss limitations of computers, specifically what they cannot do well.

Programming in C

Introduction to C

• Transition from Scratch (a block-based language) to C (a text-based language).
• Writing source code and compiling it to machine code using a compiler.
• Introduction to compiling with the make command.

Syntax and Structure

• Source Code: Human-readable code written by programmers.
• Machine Code: Binary code (0s and 1s) that the computer executes.
• Compiler: Translates source code into machine code.

Basic Program - "Hello, World!"

• First program is to print "Hello, World!" on the screen.
• Use of printf function in C as an equivalent to Scratch's "say" block.
• Syntax includes #include <stdio.h>, int main(void), printf("Hello, world\n");

Functions, Variables, and Data Types

• Functions: printf (output), get_string (input)
• Variables: Declared with a data type, e.g., string, int.
• Data Types: int (integer), float (decimal), string (text), char (single character).

Input and Output

• Getting user input: get_string, get_int from CS50 library.
• Printing formatted output using printf and format specifiers (%s, %d, %f).

Conditionals and Control Flow

If Statements

• Syntax for conditional statements: if, else if, else.
• Use of Boolean expressions for decision making.
• Comparison operators: <, >, ==.

Logical Operators

• && (logical AND)
• || (logical OR)

Scope

• Variables are only accessible within their defined scope, determined by curly braces {}.

Loops

While Loops

• Used to repeat actions while a condition is true.
• Example: Using a counter to repeat actions a specified number of times.

For Loops

• More concise than while loops, consists of initialization, condition, and increment.
• Example: for(int i = 0; i < 3; i++) to repeat three times.

Do-while Loops

• Executes the loop body at least once before checking the condition.

Creating Functions

• Define custom functions to encapsulate and reuse code.
• Function definition includes return type, name, parameters, and body.
• Example: Creating a meow function to print "meow" multiple times.

Limitations of Computers

Integer Overflow

• Limited by the number of bits used to represent numbers.
• Example: 32-bit integers can count only up to 4 billion.

Floating Point Imprecision

• Limits in representing real numbers accurately due to finite memory.
• Example: 1/3 in float results in rounding errors when extended beyond precision.

Real-World Implications

• Historical and practical issues with integer overflow in software (Y2K, 2038 problem).
• Examples from gaming (Pac-Man, Donkey Kong) and real-life systems (Boeing 787).

Conclusion

• Introduction to C programming with emphasis on learning through practice.
• Exploration of both the power and limitations of programming and computers.