Fixing “Not Declared in This Scope” Errors

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1Your First Compile-Run Loop in C++2Compiling With an Explicit C++ Standard Flag 3Running the Executable and Reading Output as Evidence 4Printing Text and Numbers: \n vs std::endl 5Edit, Recompile, Rerun: Avoiding the “Why Didn’t It Change?” Trap 6Your First Compiler Diagnostic: Fixing a Missing Semicolon

7An int Variable: Name a Value and Watch It Change 8When You Need Fractions: double and Non-Integer Results 9True or False: bool and Printing Conditions 10One Character: char and How It Differs From int 11The Uninitialized Variable Bug: Always Give a Starting Value 12Named Constants: const for Values That Should Not Change 13Trace-Then-Run Practice: Predict Exact Output From Assignments

14Your First Interactive Read: std::cin >> x 15Reading Two Numbers and Printing Intermediate Values 16Whitespace and the Token Model 17Checking Whether Input Succeeded 18When Input Fails: Non-Numeric Text for an int 19Practice: Trace Tokens to Printed Output

20Addition and Subtraction You Can Trace 21Multiplication, Division, and the Integer Division Surprise 22Remainder (%) and Even/Odd Without Branching 23Parentheses: Make the Expression Match Your Intent 24Compound Assignment (+=): Updating State Clearly 25Fixing Wrong Math: Operators and Parentheses Debug Drill

26Seeing Comparisons as True or False 27Storing Conditions in bool Variables 28Logical NOT: Inverting a Condition 29Logical AND: Two Conditions Must Both Be True 30Logical OR: Either Condition Can Be True 31Debugging = vs == in Conditions

32A One-Way Decision With if 33Two-Way Decisions With if and else 34Multi-Way Decisions With else-if Chains 35Braces, Block Scope, and Variables Inside Branches 36switch for Menu-Style Choices 37default and Handling Unexpected Choices 38Debugging Branching: Mismatched Braces and Missing break

39A while Loop That Makes Progress 40Sentinel-Controlled while Loops With std::cin 41for Loops as Count-Controlled Repetition 42Running Totals: Sum in a Loop You Can Trace 43Off-by-One: i < n vs i <= n 44Stopping Early With break 45Skipping Work With continue 46Choosing while vs for: A Practical Decision Rule

47Calling a Function and Using the Return Value 48Defining a Function That Returns a Value (No Parameters)49One-Parameter Functions: Tracing Argument to Parameter to Return 50Void Functions: Doing Work Without Returning a Value 51Parameters vs. Arguments: Proving It With Prints 52Composing Functions: Calling One Function From Another 53Forward Declarations: Fixing Call-Before-Definition 54Function Signature Mistakes: Wrong Return Type and Missing Return

55Block Scope: Names Live Inside Braces 56Making a Temporary Scope With Extra Braces 57Function Scope: Same Name, Different Function 58Shadowing: When a New Variable Hides an Old One

59Fixing “Not Declared in This Scope” Errors

60Tracing Scope to Predict Output

61Pass-by-Value: Why Changes Don’t Stick 62Reference Variables: An Alias That Changes the Original 63Reference Parameters: Let a Function Modify the Caller 64Return a Value vs Mutate by Reference 65Multiple Parameters: Which Ones Can Change?66Debugging: The Missing & Bug in Function Parameters 67Const References for Read-Only Parameters (Optional Enrichment)68Trace-by-Hand: Predict What Changes After Mixed Calls

69Fixed-Size Arrays: What You Get and What You Don’t 70Building a std::vector From Input With push_back 71Index-Based Iteration: size(), v[i], and a Traceable Sum 72Out-of-Range Indexing: The Off-by-One Bug in Vectors 73Range-Based for: Iterating Values Without Index Math 74Modifying Vector Elements: Indexes vs References in Range Loops 75Vectors Hold Types: Using std::vector<double> for Real Numbers 76Practice: Converting an Array Program to std::vector

77Your First std::string: Print and Concatenate 78Length and Indexing: Looking Inside a String 79Comparing Strings: Equality and Simple Ordering 80Token Input Into std::string: Words Stop at Whitespace 81Line Input With std::getline: Spaces Included 82The >> Then getline Bug: Why You Get an Empty Line 83Legacy Note: Why This Path Uses std::string by Default

84From a Value to an Address: Your First int*85nullptr and the ‘Maybe Points to Something’ Idea 86Reseating a Pointer: Point to x, Then Point to y 87References vs Pointers: Alias vs Nullable Indirection 88The Null-Dereference Bug Class (and the Guard Pattern)89What We Are Not Doing: new/delete and Why This Course Avoids Them

90A Record Type With struct and Observable Output 91A Vector of Records and Traceable Iteration 92A Minimal Class That Enforces a Simple Rule 93Using One <algorithm> Tool Instead of Hand-Rolled Loops 94Splitting Code Into .hpp and .cpp Without Breaking It 95Compiling Objects and Linking an Executable (The Real Build Loop)96Warnings as Feedback: Turning On -Wall -Wextra -pedantic 97Fixing a Compile Error: Missing Includes and Wrong Types 98Fixing a Link Error: Undefined Reference to a Missing Definition 99Optional: -g and a Tiny gdb Loop (break, run, next, print)

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Modern C++ Programming for Beginners
Fixing “Not Declared in This Scope” Errors