2.5

2.5 Lab - Getting User Input in C

Introduction

In this lab, you will learn how to get input from the user using the scanf function in C. You will write a program that prompts the user for their name and age, captures the input, and then displays a message using the provided information. This is an important step in understanding how programs interact with users in real-world applications.

Objectives

By the end of this lab, you will be able to:

Understand how to use the scanf function to read user input in C.
Write a program that accepts input from the user.
Compile and run the program in a Linux environment using gcc.
Display output based on the user's input.

Lab Steps

Step 1: Open the Terminal

Open the terminal on your Linux machine.
Navigate to your working directory, or use the directory you created in the previous lab:
```
cd c_programs
```

Step 2: Create a New C Program

Use the Nano editor to create a new C program file:
```
nano user_input.c
```

In the Nano editor, type the following code to prompt the user for their name and age:

#include <stdio.h>

int main() {
    char name[50];
    int age;

    // Ask the user for their name
    printf("Enter your name: ");
    // Get the user's name (string input)
    scanf("%s", name);

    // Ask the user for their age
    printf("Enter your age: ");
    // Get the user's age (integer input)
    scanf("%d", &age);

    // Display the user's input
    printf("Hello, %s! You are %d years old.\n", name, age);

    return 0;
}

Save the file by pressing CTRL + O, then press Enter. Exit the Nano editor by pressing CTRL + X.

Step 3: Compile the Program Using gcc

To compile your C program, use the gcc compiler. Run the following command:
```
gcc user_input.c -o user_input
```
If there are no errors, the command will create an executable file named user_input. You can list the files to confirm:
```
ls
```
You should see user_input in the list.

Step 4: Run the Program

Now that the program is compiled, run it by typing:
```
./user_input
```
The program will prompt you for your name and age. For example:
```
Enter your name: John
Enter your age: 25
```
After entering the name and age, the program will display a message like this:
```
Hello, John! You are 25 years old.
```

Step 5: Experimenting with Different Inputs

Try running the program multiple times with different names and ages to see how it responds. For example:
```
Enter your name: Alice
Enter your age: 30
```
The program should display:
```
Hello, Alice! You are 30 years old.
```

Step 6: Understanding the Code

char name[50];: This line declares a string (an array of characters) to store the user’s name. The maximum length of the name is set to 50 characters.
int age;: This declares an integer variable to store the user’s age.
scanf("%s", name);: This function reads the user’s name from the input.
scanf("%d", &age);: This reads the user’s age. Note the & symbol before the variable age — it is required to provide the memory address of the variable to scanf.
printf("Hello, %s! You are %d years old.\n", name, age);: This prints the greeting message, using %s to display the string (name) and %d to display the integer (age).

Summary

In this lab, you learned how to use the scanf function to get input from the user in C. You built a program that asks the user for their name and age and then prints a message based on their input. This is a crucial concept, as user interaction forms the foundation of many C programs. By using scanf, you can handle different types of input and create interactive programs that respond to user-provided data.