Introduction to Programming in C

📘 Input and Output Functions in C

Input and output (I/O) are essential to make your C programs interactive. Without I/O functions, a program would only process fixed data and produce output without user involvement. In C, we primarily use printf() to display information and scanf() to take input from the user.

🔸 What is printf()?

printf() is used to send formatted output to the screen. It's part of the standard I/O library in C (stdio.h).

#include <stdio.h>

int main() {
    printf("Welcome to UdaanPath!\n");
    return 0;
}

✅ Format Specifiers in printf():

• %d – for integers (e.g., int age = 20;)
• %f – for floating-point values (e.g., float pi = 3.14;)
• %c – for single characters (e.g., char grade = 'A';)
• %s – for strings (e.g., char name[] = "Rahul";)
• %.2f – to display float with 2 decimal places

✨ Special Escape Sequences:

• \n – New line
• \t – Tab space
• \\ – Backslash
• \" – Double quote

🔸 What is scanf()?

scanf() is used to take input from the user. It scans the input and stores it in variables via pointers (using & symbol).

#include <stdio.h>

int main() {
    int age;
    printf("Enter your age: ");
    scanf("%d", &age);
    printf("You are %d years old.\n", age);
    return 0;
}

📌 Key Points:

• scanf() needs the address of the variable (& symbol).
• The format specifier must match the data type of the variable.
• Whitespace, newlines, and characters affect how scanf() reads inputs.

💡 Taking Multiple Inputs

int a, b;
printf("Enter two numbers: ");
scanf("%d %d", &a, &b);
printf("Sum = %d\n", a + b);

📚 Input and Output for Strings

Use scanf("%s", str) to read a string (till whitespace). For full sentence input, use fgets().

char name[50];
printf("Enter your name: ");
scanf("%s", name);
printf("Hello %s, welcome to UdaanPath!\n", name);

🛠 Tip: Use fgets() for full lines

char line[100];
printf("Enter a sentence: ");
fgets(line, sizeof(line), stdin);
printf("You entered: %s", line);

🔍 Comparison Table

🧪 Practice Exercises

1. Write a program to take name, age, and salary from the user and print them back.
2. Build a calculator that takes two numbers and displays their sum, difference, product, and division.
3. Write a program that takes a full name using fgets() and displays a greeting message.

🧠 Summary

• printf() is used for output. It supports format specifiers to print variables.
• scanf() is used for input. Use & before variables to store input values.
• String input should ideally use fgets() for safety and completeness.

✅ Coming Next

In the next chapter, we’ll dive into Operators and Expressions — the foundation of decision-making and calculations in C.