Correct way to use scanf function in C language

How to correctly use the scanf function in C language

Introduction:
In C language, the scanf function is one of the commonly used input functions, which allows users to Enter data from the keyboard. However, due to some subtle differences in some features and usage of the scanf function, it may easily cause some problems. This article will introduce how to use the scanf function correctly and related precautions, and attach specific code examples.

1. Basic usage of the scanf function:
The basic usage of the scanf function is very simple. It uses a format string as a parameter, and the format string specifies the type and format of the input data. For example, "%d" means entering an integer, "%f" means entering a single-precision floating point number, "%s" means entering a string, and so on.

Sample code 1:

#include <stdio.h>
int main() {
    int num;
    printf("请输入一个整数：");
    scanf("%d", &num);  // 输入一个整数
    printf("您输入的整数是：%d
", num);
    return 0;
}

2. Return value of scanf function and buffer problem:
scanf function returns the number of successfully read data when it successfully reads data. If If the read fails, EOF is returned. It is important to note that when the read fails, the scanf function leaves the error in the input buffer. This may cause subsequent input operations to produce unexpected results.

Sample code 2:

#include <stdio.h>
int main() {
    int num;
    char ch;
    printf("请输入一个整数和一个字符：");
    scanf("%d", &num);  // 输入一个整数
    scanf(" %c", &ch);  // 输入一个字符（注意前面的空格）
    printf("您输入的整数是：%d
", num);
    printf("您输入的字符是：%c
", ch);
    return 0;
}

There is a space in front of the second scanf function in the above code, the purpose is to eliminate the newline character left in the input buffer by the previous scanf function. Otherwise, the second scanf function will read the newline character in the buffer and produce incorrect results.

3. Format string issues in the scanf function:
Be very careful when using format strings. Wrong format strings may cause the program to crash or produce incorrect results.

Sample code 3:

#include <stdio.h>
int main() {
    int num1, num2;
    printf("请输入两个整数：");
    scanf("%d%d", &num1, &num2);  // 输入两个整数
    printf("您输入的两个整数是：%d和%d
", num1, num2);
    return 0;
}

The format string "%d%d" in the first scanf function in the above code means reading two integers, using spaces and tabs Or newlines separate them. Failure to properly separate the two integers during input will result in an input error.

4. Input restriction issues in the scanf function:
The scanf function uses space, tab or newline character as the input terminator by default. If you need to control the length of the input, you can use modifiers in the format string.

Sample code 4:

#include <stdio.h>
int main() {
    char name[20];
    printf("请输入您的名字（不超过20个字符）：");
    scanf("%19s", name);  // 输入一个字符串，最多19个字符
    printf("您的名字是：%s
", name);
    return 0;
}

The modifier "s" in the above code means that a maximum of 19 characters can be entered to prevent overflow. Note that array subscripts start at 0, so the length of "s" is 19 instead of 20.

Conclusion:
The correct use of the scanf function requires attention to return value and buffer issues, format string issues, and input restriction issues. In actual programming, please pay attention to follow these guidelines and make appropriate modifications as needed. Only by using the scanf function correctly can we better write high-quality and robust C language programs.

The above is an introduction on how to correctly use the scanf function in C language. I hope it will be helpful to you. thanks for reading!

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