Conditional statement usage and examples in C++

C, as a high-level programming language, has a variety of flow control statements to implement the decision-making structure and loop structure of the program. Among them, the conditional statement is one of the most commonly used statements in C programming. It determines the execution path of the program by judging whether the condition is met. This article will introduce the usage and examples of conditional statements in C in detail to help readers better understand and apply this syntax.

1. Basic syntax of conditional statements

Conditional statements in C mainly include three types: if statement, if else statement and switch statement. Their basic syntax is as follows:

1. if statement:

if (condition)
{
    // 如果条件成立，执行这里的语句
}

The meaning of the if statement is: if the condition is true, execute the statement in {}.

2. if else statement:

if (condition)
{
    // 如果条件成立，执行这里的语句
}
else
{
    // 如果条件不成立，执行这里的语句
}

The meaning of the if else statement is: if the condition is true, execute the statement in if{}; otherwise, execute else{} statements in.

3. switch statement:

switch (expression)
{
    case value1:
        // 如果expression等于value1执行这里的语句
        break;

    case value2:
        // 如果expression等于value2执行这里的语句
        break;

    default:
        // 如果expression不等于value1和value2执行这里的语句
        break;
}

The meaning of the switch statement is: according to the value of expression, execute the corresponding case statement. If there is no match, execute default{} statements in. Note that a break statement must be added after each case to jump out of the switch statement.

2. Examples of conditional statements

1. Usage examples of if statements

#include <iostream>
using namespace std;

int main()
{
    int a = 10;
    if (a > 0)
    {
        cout << "a是正数" << endl;
    }
    else
    {
        cout << "a是负数" << endl;
    }

    return 0;
}

Explanation: Define an integer variable a and assign it a value of 10, If a is greater than 0, output "a is a positive number", otherwise output "a is a negative number".

Output result: a is a positive number.

2. Usage example of if else statement

#include <iostream>
using namespace std;

int main()
{
    int score = 80;
    if (score >= 90)
    {
        cout << "A" << endl;
    }
    else if (score >= 80)
    {
        cout << "B" << endl;
    }
    else if (score >= 70)
    {
        cout << "C" << endl;
    }
    else if (score >= 60)
    {
        cout << "D" << endl;
    }
    else
    {
        cout << "F" << endl;
    }

    return 0;
}

Explanation: Define an integer variable score and assign it a value of 80. If the score is greater than or equal to 90, output "A"; if If the score is greater than or equal to 80 and less than 90, "B" is output; and so on, if none of the conditions are met, "F" is output.

Output result: B.

3. Use examples of switch statement

#include <iostream>
using namespace std;

int main()
{
    char grade = 'B';
    switch (grade)
    {
        case 'A':
            cout << "优秀" << endl;
            break;

        case 'B':
            cout << "良好" << endl;
            break;

        case 'C':
            cout << "及格" << endl;
            break;

        default:
            cout << "不及格" << endl;
            break;
    }

    return 0;
}

Explanation: Define a character variable grade and assign it a value of 'B', and execute the corresponding case statement based on its value. If If none of them match, the statement in default{} will be executed and "failed" will be output.

Output result: Good.

3. Notes in practice

1. If there is only one statement in the if statement or if else statement, the braces can be omitted, but this is not recommended.
2. Each case in the switch statement must be followed by a break statement, otherwise the next case statement will continue to be executed until a break statement is encountered.
3. When using conditional statements, pay attention to the consistency of variable types to avoid type conversion errors and unpredictable results.

In short, the conditional statement is one of the very important control structures in the program, which can select different execution paths according to different conditions. Mastering the usage and application of various conditional statements in C can make programming more flexible and efficient.

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