PROJECTENGRAM

CONDITIONAL STATEMENTS

Conditional Statements

Tags: #◇Code Snippets #◇CCPROG1 #◇Control Flow #◇C #◇M5

◇Overview

Conditional statements, or selection structures, allow a program to make decisions and execute different blocks of code based on whether a specified condition evaluates to true or false.

◇Key Definitions

Condition: A logical expression that evaluates to true (non-zero) or false (zero). if Statement: Executes a block of code if its condition is true. else Statement: Executes a block of code if the preceding if condition is false. switch Statement: Allows a variable to be tested for equality against a list of values.

◇Code Implementation

『』
C
#include <stdio.h>

int main() {
    int grade = 85;
    
    // if-else if-else structure
    if (grade >= 90) {
        printf("A\n");
    } else if (grade >= 80) {
        printf("B\n");
    } else if (grade >= 70) {
        printf("C\n");
    } else {
        printf("F\n");
    }
    
    // switch statement
    char letter = 'B';
    switch (letter) {
        case 'A':
            printf("Excellent\n");
            break;
        case 'B':
            printf("Good\n");
            break;
        default:
            printf("Needs Improvement\n");
    }
    
    return 0;
}

◇Syntax Breakdown

if (condition): The code block inside {} runs if condition is true. else if (condition): Checked only if the previous if was false. switch(variable): Evaluates variable. case 'X':: If variable equals 'X', execute following code. break;: Exits the switch block, preventing fall-through to the next case.

◇Common Pitfalls

Forgetting the break; statement in a switch, which causes "fall-through" execution. Using = (assignment) instead of == (equality check) inside an if condition. E.g., if (x = 5) evaluates to true because 5 is non-zero, and it changes x to 5.

◇References & Navigation

CONFIRMATION // 理解度の確認

ACTIVE RECALL VERIFICATION

Select an answer to verify conceptual comprehension and reveal the technical rationale.

Q1

What is the output of the following C code snippet if int x = 0;?
if (x = 5) printf("True"); else printf("False");

Q2

In a C switch statement, what happens when a matching case block omits the break; statement?

Q3

Which of the following data types CANNOT be used as the controlling expression of a switch statement in standard C?

Q4

In an if - else if - else ladder, when is the final else block executed?

Q5

With which if does the else pair in the nested statement if (a > 0) if (b > 0) printf("1"); else printf("2");?