C Notes

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getchar() and putchar() in C Programming

Learn character input/output functions getchar() and putchar() in C. Understand how they work, their relationship with stdin/stdout, buffered I/O, and practical examples for character processing.

When you need to read or write a single character at a time, getchar() and putchar() are your go-to functions. They're simpler than scanf() and printf(), faster for character-by-character processing, and form the building blocks for many text-processing programs. Understanding these functions also helps you grasp how buffered I/O works in C.

putchar() — Write a Single Character

putchar() writes a single character to standard output (the screen). It's declared in <stdio.h>.

c example

int putchar(int character);

It takes an integer (the ASCII value of the character) and returns the character written, or EOF on error.

Example

#include <stdio.h> int main() { // Print individual characters putchar('H'); putchar('e'); putchar('l'); putchar('l'); putchar('o'); putchar('\n'); // Using ASCII values putchar(65); // 'A' putchar(66); // 'B' putchar(67); // 'C' putchar('\n'); // Print a string character by character char msg[] = "Welcome to C!"; int i = 0; while (msg[i] != '\0') { putchar(msg[i]); i++; } putchar('\n'); return 0; }

Output

Hello
ABC
Welcome to C!

getchar() — Read a Single Character

getchar() reads a single character from standard input (keyboard). It waits for the user to press Enter before processing input (line-buffered).

c example

int getchar(void);

It returns the character read as an int, or EOF if end of input is reached.

c example

#include <stdio.h>

int main() {
    char ch;

    printf("Enter a character: ");
    ch = getchar();

    printf("You entered: ");
    putchar(ch);
    putchar('\n');

    printf("ASCII value: %d\n", ch);

    return 0;
}

Output

Enter a character: A
You entered: A
ASCII value: 65

Why getchar() Returns int, Not char

This is a common question. getchar() returns int because it needs to return both valid characters (0-255) AND the special value EOF (typically -1). If it returned char, you couldn't distinguish between a valid character with value 255 and EOF.

c example

#include <stdio.h>

int main() {
    int ch;  // Must be int, not char!

    printf("Enter text (Ctrl+D to end on Linux, Ctrl+Z on Windows):\n");

    while ((ch = getchar()) != EOF) {
        putchar(ch);
    }

    printf("\nEnd of input detected\n");

    return 0;
}

Output

Enter text (Ctrl+D to end on Linux, Ctrl+Z on Windows):
Hello World
Hello World
Bye
Bye

End of input detected

Buffered I/O Behavior

Standard input in C is typically line-buffered. This means getchar() doesn't receive characters one-by-one as you type them — it waits until you press Enter, then delivers the entire line one character at a time.

Example

#include <stdio.h> int main() { int ch; int count = 0; printf("Type something and press Enter:\n"); // Even though you type all chars at once, // getchar() processes them one at a time after Enter while ((ch = getchar()) != '\n') { printf("Character %d: '%c' (ASCII: %d)\n", ++count, ch, ch); } printf("Total characters: %d\n", count); return 0; }

Output

Type something and press Enter:
Hi!
Character 1: 'H' (ASCII: 72)
Character 2: 'i' (ASCII: 105)
Character 3: '!' (ASCII: 33)
Total characters: 3

Practical Examples

Counting Characters, Words, and Lines

Example

#include <stdio.h> int main() { int ch; int chars = 0, words = 0, lines = 0; int inWord = 0; printf("Enter text (Ctrl+D/Ctrl+Z to end):\n"); while ((ch = getchar()) != EOF) { chars++; if (ch == '\n') { lines++; } if (ch == ' ' || ch == '\n' || ch == '\t') { inWord = 0; } else if (!inWord) { inWord = 1; words++; } } printf("\nCharacters: %d\n", chars); printf("Words: %d\n", words); printf("Lines: %d\n", lines); return 0; }

Output

Enter text (Ctrl+D/Ctrl+Z to end):
Hello World
This is C programming

Characters: 33
Words: 5
Lines: 2

Convert Lowercase to Uppercase

c example

#include <stdio.h>

int main() {
    int ch;

    printf("Enter text (press Enter to process):\n");

    while ((ch = getchar()) != '\n') {
        if (ch >= 'a' && ch <= 'z') {
            putchar(ch - 32);  // Convert to uppercase
        } else {
            putchar(ch);
        }
    }
    putchar('\n');

    return 0;
}

Output

Enter text (press Enter to process):
hello World 123!
HELLO WORLD 123!

Copy Input to Output (Character Echo)

c example

#include <stdio.h>

int main() {
    int ch;

    printf("Type text (Ctrl+D/Ctrl+Z to stop):\n");
    printf("Each line will be echoed back:\n\n");

    while ((ch = getchar()) != EOF) {
        putchar(ch);
    }

    return 0;
}

Remove Consecutive Duplicate Characters

c example

#include <stdio.h>

int main() {
    int ch, prev = -1;

    printf("Enter text with duplicates:\n");

    while ((ch = getchar()) != '\n') {
        if (ch != prev) {
            putchar(ch);
        }
        prev = ch;
    }
    putchar('\n');

    return 0;
}

Output

Enter text with duplicates:
aaabbcccdddeee
abcde

Count Vowels and Consonants

Example

#include <stdio.h> int main() { int ch; int vowels = 0, consonants = 0, digits = 0, others = 0; printf("Enter a line of text:\n"); while ((ch = getchar()) != '\n') { if ((ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z')) { ch = (ch >= 'A' && ch <= 'Z') ? ch + 32 : ch; // to lowercase if (ch == 'a' || ch == 'e' || ch == 'i' || ch == 'o' || ch == 'u') { vowels++; } else { consonants++; } } else if (ch >= '0' && ch <= '9') { digits++; } else { others++; } } printf("Vowels: %d\n", vowels); printf("Consonants: %d\n", consonants); printf("Digits: %d\n", digits); printf("Others: %d\n", others); return 0; }

Output

Enter a line of text:
Hello World 123!
Vowels: 3
Consonants: 7
Digits: 3
Others: 3

getchar() for Pausing Program Execution

A common use of getchar() is to pause the program until the user presses Enter:

c example

#include <stdio.h>

int main() {
    printf("Processing data...\n");
    printf("Step 1 complete.\n");

    printf("\nPress Enter to continue...");
    getchar();

    printf("Step 2 complete.\n");
    printf("All done!\n");

    return 0;
}

Output

Processing data...
Step 1 complete.

Press Enter to continue...
Step 2 complete.
All done!

getchar() vs scanf("%c") vs getch()

Function	Header	Buffered	Echo	Newline handling
`getchar()`	`<stdio.h>`	Yes	Yes	Stays in buffer
`scanf("%c")`	`<stdio.h>`	Yes	Yes	Can skip with space
`getch()`	`<conio.h>`	No	No	Platform-specific
`getche()`	`<conio.h>`	No	Yes	Platform-specific

c example

#include <stdio.h>

int main() {
    char ch1, ch2;

    // getchar() reads character including whitespace
    printf("Enter first char: ");
    ch1 = getchar();

    // Must consume the leftover newline!
    while (getchar() != '\n');  // Flush buffer

    printf("Enter second char: ");
    ch2 = getchar();

    printf("You entered: '%c' and '%c'\n", ch1, ch2);

    return 0;
}

Output

Enter first char: A
Enter second char: B
You entered: 'A' and 'B'

Flushing the Input Buffer

After using getchar() or scanf(), leftover characters (especially \n) can cause issues. Here's how to flush the buffer:

c example

#include <stdio.h>

void flushInput() {
    int c;
    while ((c = getchar()) != '\n' && c != EOF);
}

int main() {
    int num;
    char ch;

    printf("Enter a number: ");
    scanf("%d", &num);

    flushInput();  // Clear the leftover newline

    printf("Enter a character: ");
    ch = getchar();

    printf("Number: %d, Character: '%c'\n", num, ch);

    return 0;
}

Output

Enter a number: 42
Enter a character: X
Number: 42, Character: 'X'

Interview Questions

Q1: Why does getchar() return int instead of char?

getchar() returns int to accommodate both valid character values (0-255) and the special EOF value (typically -1). If it returned char, there would be no way to distinguish between EOF and a valid character with value 255 (on systems where char is unsigned) or -1 (on systems where char is signed).

Q2: What is the difference between getchar() and scanf("%c")?

Both read a single character, but: (1) getchar() takes no arguments and always reads the next character including whitespace; (2) scanf(" %c", &ch) with a leading space skips whitespace characters. Also, getchar() returns the character as an int, while scanf stores it via a pointer.

Q3: How does line buffering affect getchar()?

Standard input is line-buffered by default. This means characters aren't delivered to getchar() until the user presses Enter. All characters typed on the line are buffered, and subsequent getchar() calls read from this buffer without waiting for more input — until the buffer is empty.

Q4: How do you properly read two characters using getchar()?

After reading the first character, you must consume the newline left by pressing Enter: either call getchar() again to discard it, or use a loop while(getchar() != '\n'); to flush the buffer. Then the second getchar() will correctly wait for new input.

Q5: Can putchar() print integers or strings?

No directly. putchar() prints a single character. To print an integer, you'd need to convert it to characters digit by digit. To print a string, loop through each character: while(*str) putchar(*str++);. For anything beyond single characters, use printf().

Summary

getchar() reads one character from stdin; putchar() writes one character to stdout
getchar() returns int (not char) to distinguish valid characters from EOF
Standard input is line-buffered — characters are delivered only after Enter is pressed
Always check for EOF in loops that read until end-of-input
The leftover newline after input is a common source of bugs — flush the buffer
These functions are ideal for character-by-character text processing programs
They're simpler and faster than scanf/printf for single character operations

Exam Focus

Revise definitions, diagrams, examples, and short-answer points for getchar() and putchar() in C Programming.

Interview Use

Prepare one clear explanation, one practical example, and one common mistake for this C Programming topic.

Search Terms

c-programming, c programming, programming, input, output, getchar, and, putchar

Continue learning this concept

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PreviousFormat Specifiers in C - Complete Reference Nextgets() and puts() in C Programming

C Notes

getchar() and putchar() in C Programming

Learn character input/output functions getchar() and putchar() in C. Understand how they work, their relationship with stdin/stdout, buffered I/O, and practical examples for character processing.

putchar() — Write a Single Character

putchar() writes a single character to standard output (the screen). It's declared in <stdio.h>.

c example

int putchar(int character);

It takes an integer (the ASCII value of the character) and returns the character written, or EOF on error.

Example

Output

Hello
ABC
Welcome to C!

getchar() — Read a Single Character

getchar() reads a single character from standard input (keyboard). It waits for the user to press Enter before processing input (line-buffered).

c example

int getchar(void);

It returns the character read as an int, or EOF if end of input is reached.

c example

#include <stdio.h>

int main() {
    char ch;

    printf("Enter a character: ");
    ch = getchar();

    printf("You entered: ");
    putchar(ch);
    putchar('\n');

    printf("ASCII value: %d\n", ch);

    return 0;
}

Output

Enter a character: A
You entered: A
ASCII value: 65

Why getchar() Returns int, Not char

c example

#include <stdio.h>

int main() {
    int ch;  // Must be int, not char!

    printf("Enter text (Ctrl+D to end on Linux, Ctrl+Z on Windows):\n");

    while ((ch = getchar()) != EOF) {
        putchar(ch);
    }

    printf("\nEnd of input detected\n");

    return 0;
}

Output

Enter text (Ctrl+D to end on Linux, Ctrl+Z on Windows):
Hello World
Hello World
Bye
Bye

End of input detected

Buffered I/O Behavior

Example

Output

Type something and press Enter:
Hi!
Character 1: 'H' (ASCII: 72)
Character 2: 'i' (ASCII: 105)
Character 3: '!' (ASCII: 33)
Total characters: 3

Practical Examples

Counting Characters, Words, and Lines

Example

Output

Enter text (Ctrl+D/Ctrl+Z to end):
Hello World
This is C programming

Characters: 33
Words: 5
Lines: 2

Convert Lowercase to Uppercase

c example

#include <stdio.h>

int main() {
    int ch;

    printf("Enter text (press Enter to process):\n");

    while ((ch = getchar()) != '\n') {
        if (ch >= 'a' && ch <= 'z') {
            putchar(ch - 32);  // Convert to uppercase
        } else {
            putchar(ch);
        }
    }
    putchar('\n');

    return 0;
}

Output

Enter text (press Enter to process):
hello World 123!
HELLO WORLD 123!

Copy Input to Output (Character Echo)

c example

#include <stdio.h>

int main() {
    int ch;

    printf("Type text (Ctrl+D/Ctrl+Z to stop):\n");
    printf("Each line will be echoed back:\n\n");

    while ((ch = getchar()) != EOF) {
        putchar(ch);
    }

    return 0;
}

Remove Consecutive Duplicate Characters

c example

#include <stdio.h>

int main() {
    int ch, prev = -1;

    printf("Enter text with duplicates:\n");

    while ((ch = getchar()) != '\n') {
        if (ch != prev) {
            putchar(ch);
        }
        prev = ch;
    }
    putchar('\n');

    return 0;
}

Output

Enter text with duplicates:
aaabbcccdddeee
abcde

Count Vowels and Consonants

Example

Output

Enter a line of text:
Hello World 123!
Vowels: 3
Consonants: 7
Digits: 3
Others: 3

getchar() for Pausing Program Execution

A common use of getchar() is to pause the program until the user presses Enter:

c example

#include <stdio.h>

int main() {
    printf("Processing data...\n");
    printf("Step 1 complete.\n");

    printf("\nPress Enter to continue...");
    getchar();

    printf("Step 2 complete.\n");
    printf("All done!\n");

    return 0;
}

Output

Processing data...
Step 1 complete.

Press Enter to continue...
Step 2 complete.
All done!

getchar() vs scanf("%c") vs getch()

Function	Header	Buffered	Echo	Newline handling
`getchar()`	`<stdio.h>`	Yes	Yes	Stays in buffer
`scanf("%c")`	`<stdio.h>`	Yes	Yes	Can skip with space
`getch()`	`<conio.h>`	No	No	Platform-specific
`getche()`	`<conio.h>`	No	Yes	Platform-specific

c example

#include <stdio.h>

int main() {
    char ch1, ch2;

    // getchar() reads character including whitespace
    printf("Enter first char: ");
    ch1 = getchar();

    // Must consume the leftover newline!
    while (getchar() != '\n');  // Flush buffer

    printf("Enter second char: ");
    ch2 = getchar();

    printf("You entered: '%c' and '%c'\n", ch1, ch2);

    return 0;
}

Output

Enter first char: A
Enter second char: B
You entered: 'A' and 'B'

Flushing the Input Buffer

After using getchar() or scanf(), leftover characters (especially \n) can cause issues. Here's how to flush the buffer:

c example

#include <stdio.h>

void flushInput() {
    int c;
    while ((c = getchar()) != '\n' && c != EOF);
}

int main() {
    int num;
    char ch;

    printf("Enter a number: ");
    scanf("%d", &num);

    flushInput();  // Clear the leftover newline

    printf("Enter a character: ");
    ch = getchar();

    printf("Number: %d, Character: '%c'\n", num, ch);

    return 0;
}

Output

Enter a number: 42
Enter a character: X
Number: 42, Character: 'X'

Interview Questions

Q1: Why does getchar() return int instead of char?

Q2: What is the difference between getchar() and scanf("%c")?

Q3: How does line buffering affect getchar()?

Q4: How do you properly read two characters using getchar()?

Q5: Can putchar() print integers or strings?

Summary

getchar() reads one character from stdin; putchar() writes one character to stdout
getchar() returns int (not char) to distinguish valid characters from EOF
Standard input is line-buffered — characters are delivered only after Enter is pressed
Always check for EOF in loops that read until end-of-input
The leftover newline after input is a common source of bugs — flush the buffer
These functions are ideal for character-by-character text processing programs
They're simpler and faster than scanf/printf for single character operations

Exam Focus

Revise definitions, diagrams, examples, and short-answer points for getchar() and putchar() in C Programming.

Interview Use

Prepare one clear explanation, one practical example, and one common mistake for this C Programming topic.

Search Terms

c-programming, c programming, programming, input, output, getchar, and, putchar

Continue learning this concept

PreviousFormat Specifiers in C - Complete Reference Nextgets() and puts() in C Programming