Input or Ouput (I/O) in C language

Input and output is key operations in the software development. It helps to interact with user.

While dealing with input-output operations, two important streams comes into picture. These are:

• Standard Input (stdin): It is used for taking input from devices such as the keyboard as a data stream.
• Standard Output (stdout): It is used for giving output to a device such as a monitor.

There are many built-in functions available in C to perform input-output operations.

Reading Character

getchar() function can be used to read a single character from standard input (i.e keyboard).

It’s syntax is: variable_name = getchar();

Writing Character

putchar() function is used to write characters, but one at a time to the standard output (i.e monitor).

It’s syntax is: putchar(variable_name);

#include<stdio.h>

int main()
{
  char alphabet;

  alphabet = getchar();
  putchar(alphabet);
}

// output
A // type A
A // printed by program

Formatted Input

scanf() reads the formatted input from the standard input (i.e keyboard) as per the format specified and store into the variable.

Its syntax is: scanf("format", arg1, arg2, ..., argN);

Formatted Output

printf() is one of the output function which sends formatted output to the screen (or monitor).

int radius;

printf("Enter value of radius: ");
scanf("%d", &radius);
printf("Radius = %d\n", radius);

// output
Enter value of radius: 5
Radius = 5

Format Specifiers for I/O

Example

#include<stdio.h>

int main()
{
  int num1;
  float num2, sum;

  printf("Enter value of num1 and num2(float): ");
  scanf("%d%f", &num1, &num2); // Taking multiple inputs
  printf("You entered %d and %f\n", num1, num2);

  sum = num1 + num2;
  printf("The sum of %d and %f = %f\n", num1, num2, sum);

  return 0;
}

// output
Enter value of num1 and num2(float): 10 15.5
You entered 10 and 15.500000
The sum of 10 and 15.500000 = 25.500000

But, you might want to have only two decimal places right?

Use %.2f instead of %f while printing (i.e in printf).

int num1;
float num2, sum;

printf("Enter value of num1 and num2(float): ");
scanf("%d%f", &num1, &num2); // Taking multiple inputs
printf("You entered %d and %.2f\n", num1, num2);

sum = num1 + num2;
printf("The sum of %d and %.2f = %.2f\n", num1, num2, sum);

// output
Enter value of num1 and num2(float): 10 15.5
You entered 10 and 15.50
The sum of 10 and 15.50 = 25.50