Write a program that requires the input value of x and outputs the value of y. Use (1) non-nested if statement (2) nested if statement (3) if-else statement (4) switch statement respectively.

Write a program that requires the input value of x and outputs the value of y. Use (1) non-nested if statement (2) nested if statement (3) if-else statement (4) switch statement respectively.

The selection structure is a control structure commonly used in programming languages ​​and is used to execute different code blocks based on different conditions. In C language, we usually use if statement, switch statement, etc. to implement the selection structure. This article will introduce the application of four commonly used selection structures in C language, namely non-nested if statement, nested if statement, statement. if-else statement and switch

1. Unnested if statements

The non-nestedif statement is one of the simplest selection structures and is suitable for mutually exclusive conditions. The following is an example of calculating the corresponding y value based on the input x value:

cCopy code
#include <stdio.h>

int main() {
    float x, y;

    // 输入x的值
    printf("请输入x的值：");
    scanf("%f", &x);

    // 不嵌套的if语句
    if (-5 < x && x < 0)
        y = x;
    else if (x == 0)
        y = x - 1;
    else if (0 < x && x < 10)
        y = x + 1;
    else
        printf("x的值不在定义范围内\n");

    // 输出y的值
    printf("(1) 不嵌套的if语句：y = %.2f\n", y);

    return 0;
}

In this example, based on the input x value, the program determines the interval where x is located through the non-nested if statement and calculates the corresponding y value.

2. Nested if statements

Nestedif statements can handle more complex conditional logic, but it can easily lead to unclear code structure. The following is an example of using nestedif statements:

cCopy code
// 程序代码同上，只是第二个例子的部分代码发生了变化

// 嵌套的if语句
if (-5 < x && x < 0)
    y = x;
else {
    if (x == 0)
        y = x - 1;
    else {
        if (0 < x && x < 10)
            y = x + 1;
        else
            printf("x的值不在定义范围内\n");
    }
}

// 输出y的值
printf("(2) 嵌套的if语句：y = %.2f\n", y);

In this example, the nestedif statement is used to calculate the corresponding y value based on the input x value.

3. if-else statement

if-elseThe statement is a more concise way of handling mutually exclusive conditions and is suitable for situations where each condition is mutually exclusive. The following is an example of using the if-else statement:

cCopy code
// 程序代码同上，只是第三个例子的部分代码发生了变化

// if-else语句
if (-5 < x && x < 0)
    y = x;
else if (x == 0)
    y = x - 1;
else if (0 < x && x < 10)
    y = x + 1;
else
    printf("x的值不在定义范围内\n");

// 输出y的值
printf("(3) if-else语句：y = %.2f\n", y);

In this example, the if-else statement is used to calculate the corresponding y value based on the input x value.

4. switch statement

switchThe statement is suitable for different processing of different values ​​​​of a variable. However, it should be noted that the conditional expression in the switch statement can only be of integer type or character type. The following is an example of using the switch statement:

cCopy code
// 程序代码同上，只是第四个例子的部分代码发生了变化

// switch语句
switch ((int)x) {
    case -5 ... -1:
        y = x;
        break;
    case 0:
        y = x - 1;
        break;
    case 1 ... 9:
        y = x + 1;
        break;
    default:
        printf("x的值不在定义范围内\n");
        break;
}

// 输出y的值
printf("(4) switch语句：y = %.2f\n", y);

In this example, the switch statement is used to calculate the corresponding y value based on the input x value.

Notes and extensions

• Pay attention to using logical operators in conditional expressions to ensure the correctness of the conditions.
• For the processing of floating point numbers, accuracy issues need to be taken into consideration and direct comparison of floating point numbers for equality needs to be avoided.
• switchThe conditional expression in the statement can only be an integer type or character type, not a floating point number.
• The clarity of code structure is an important consideration when choosing a structural design. Excessive nesting may make the code difficult to understand and maintain.

Selection structures are a key part of the control flow in a program, executing different code paths based on different conditions. In actual programming, choosing an appropriate selection structure according to specific situations is an important part of improving code readability and maintainability.