Usage and precautions of scanf function in C language

Usage and precautions of scanf function in C language

As one of the most commonly used input functions in C language, scanf function plays an important role in program development . It can receive user input data from the standard input stream (keyboard) and store it in the specified variable. This article will introduce the usage of the scanf function and some matters needing attention, and provide specific code examples.

1. Basic usage of the scanf function
   The prototype of the scanf function is as follows:

   int scanf(const char *format, ...);

   Among them, format is a format control string used to specify the type of input data and Format. As a variable-length parameter function, the number of parameters of the scanf function is variable, and the string format can be changed according to the specified format.

The following are some commonly used format control strings and their corresponding usage:

• %d: Read integer data , Example: scanf("%d", &num);
• %f: Read floating point data, Example: scanf("%f ", &num);
• %c: Read character data, example: scanf("%c", &ch);
• %s: Read string data, example: scanf("%s", str);
• %lf: Read Get double-precision floating point data, example: scanf("%lf", &num);

2. Sample code

Below Some sample codes are used to illustrate the usage of the scanf function:

#include <stdio.h>

int main()
{
    int age;
    char name[20];

    printf("请输入您的年龄：");
    scanf("%d", &age);

    printf("请输入您的姓名：");
    scanf("%s", name);

    printf("您的年龄是：%d，姓名是：%s
", age, name);

    return 0;
}

In the above sample code, an integer variable age and a character array name are first declared. By using the scanf function in conjunction with the printf function, the age and name input by the user are received from the standard input and output through the printf function. It should be noted that when reading a string, there is no need to use the & operator.

3. Notes

When using the scanf function, you need to pay attention to the following issues:

• Conversion qualifier: in the format control character Use the correct conversion qualifier in the string to ensure that the correct type of data is read.
• Input buffer: The scanf function will store the read data in the input buffer, and generally skip blank characters (such as spaces, newlines, etc.). However, when using the scanf function multiple times to read input, incorrect input may occur because there are still residual newlines in the buffer. This can be skipped by adding whitespace characters (spaces, tabs) to the format control string.
• Input format error handling: When the format of the input data does not match the format control string, the scanf function will report an error and return an error code. Therefore, after using the scanf function, you should check its return value to handle errors in a timely manner.
• Security issues: Since the scanf function cannot control the length of user input, when reading a string, you need to pay attention to preventing buffer overflow. You can use the fgets function instead.

By using the scanf function correctly, we can easily receive input from the user and process it accordingly. However, it should be noted that the scanf function has some security and error-prone issues, so you need to be careful when using it.

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