C++ Fundamentals 006 [Notes Version – Three Basic Structures]

Click the blueFollow usC++ Fundamentals 005 – Three Basic StructuresSequenceBranchLoop01Sequence Structure:

The sequence structure in C++ is the most fundamental control structure in programming, where the program executes statements in the order they are written, without branches, loops, or jumps. It is the simplest of the three basic structures (sequence, selection, loop), reflecting a “top-down, linear progression” execution logic..

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开始 → 语句1 → 语句2 → ... → 语句n → 结束

Although the sequence structure is simple, as the basic building block of programs, all complex logic will ultimately be decomposed into sequentially executed machine instructions.

02Branch Structure

The branch structure in C++ is the key control structure for implementing intelligent decision-making in programs. The branch structure allows the program to choose different execution paths based on conditional judgments, forming the basis for constructing complex logic.

Core Concept of Branch Structure –The branch structure (also known as the selection structure) enables the program to have “thinking” capabilities, determining the direction of code execution through conditional judgments. Unlike the linear execution of the sequence structure, the branch structure introduces differentiation in execution paths.

Comparison with Sequence Structure

Feature	Sequence Structure	Branch Structure
Execution Flow	Single linear path	Multiple path choices
Control Flow	No changes	Conditional jumps
Typical Statements	Declaration/Assignment/IO	if/switch
Complexity	Basic unit	Logical layering

01If Statement Series01Single Branch

Execution Flow: If the condition is true (non-zero), execute the code block; otherwise, skip it.

02Double Branch

Provides a clear binary execution path.

03Multiple Branches

Supports multi-condition hierarchical judgments, checking conditions in order.

02Switch Statement

Features:

• Branches based on the discrete values of an expression

• Each case should be followed by <span>break</span> to prevent fall-through

<span>default</span><span> handles unmatched cases.</span>

03Loop Structure

The loop structure is like giving the computer a set of instructions to repeat the same action until a certain condition is met. It allows the program to avoid writing a lot of repetitive code, especially suitable for tasks that need to be executed repeatedly.

🔁 Three Key Elements of Loops

Imagine making the computer count from 1 to 100; these three elements are easy to understand:

1.Loop Variable: Like a counter, for example, to record the current number, <span>i</span>.

2.Loop Condition: The rule that determines whether the loop continues, such as “<span>i</span> is less than or equal to 100″.

3.Loop Body: The specific actions to be repeated in each loop, such as “print the current number <span>i</span>” or “add <span>i</span> to a total”.

01For Loop [Counted Loop]

Features:

• ‌Deterministic Loop‌: Clearly knows the number of iterations

• ‌Three-part Control‌: Initialization, condition check, iteration update

• ‌Local Variable‌: The initialization part can declare the loop counter

02While Loop [Condition]

Features:

• ‌Pre-condition‌: Check first, then execute

• ‌Uncertain Loop‌: Suitable for situations with unknown iteration counts

• ‌Possible Zero Executions‌: If the condition is initially false, it will not execute at all

03Do-While Loop [Condition]

Features:

• ‌Post-condition‌: The loop body is executed at least once

• ‌Tail Check‌: Suitable for scenarios where execution must occur before judgment

• ‌Semicolon Ending‌: Must pay attention to syntax requirements

Loop Control Statements

Break Statement

• Immediately terminates the current loop

• Used for early exit from loop conditions

• Affects only the innermost loop

Continue Statement

• Skips the remaining part of the current iteration

• Directly enters the next loop iteration

• Does not terminate the entire loop

Control in Nested Loops

• Can use labels to specify control scope

• Break and continue default affect the innermost loop

• Proper use can optimize the performance of multi-layer loops.

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