C Input and Output

printf() — Formatted Output

printf() is the standard output function in C, defined in <stdio.h>. It prints formatted text to the console using format specifiers.

Format Specifier	Type	Example
`%d` or `%i`	int	`printf("%d", 42);`
`%f`	float	`printf("%f", 3.14f);`
`%lf`	double	`printf("%lf", 3.14);`
`%c`	char	`printf("%c", 'A');`
`%s`	string (char array)	`printf("%s", "hello");`
`%u`	unsigned int	`printf("%u", 42u);`
`%ld`	long int	`printf("%ld", 1000000L);`
`%lld`	long long int	`printf("%lld", 9999999999LL);`
`%o`	Octal	`printf("%o", 8);` â†’ 10
`%x`	Hexadecimal (lowercase)	`printf("%x", 255);` â†’ ff
`%X`	Hexadecimal (uppercase)	`printf("%X", 255);` â†’ FF
`%e`	Scientific notation	`printf("%e", 12345.6);`
`%p`	Pointer address	`printf("%p", ptr);`
`%%`	Literal % sign	`printf("100%%");`

Escape Sequences

Escape Sequence	Meaning
`\n`	Newline
`\t`	Horizontal tab
`\\`	Backslash
`\"`	Double quote
`\'`	Single quote
`\0`	Null character (string terminator)
`\r`	Carriage return
`\a`	Alert (bell)

printf with Various Format Specifiers

#include <stdio.h>

int main() {
    int    age    = 25;
    float  price  = 9.99f;
    double pi     = 3.14159265;
    char   grade  = 'A';
    char   name[] = "Alice";

    printf("Name:   %s\n",  name);
    printf("Age:    %d\n",  age);
    printf("Grade:  %c\n",  grade);
    printf("Price:  %.2f\n", price);   // 2 decimal places
    printf("Pi:     %.4lf\n", pi);     // 4 decimal places

    // Width and alignment
    printf("\n%-10s %5d\n", "Alice",  25);  // left-align name, right-align age
    printf("%-10s %5d\n",  "Bob",    30);
    printf("%-10s %5d\n",  "Charlie", 22);

    // Hex and octal
    printf("\n255 in hex:   %x\n", 255);   // ff
    printf("255 in octal: %o\n",  255);   // 377
    printf("Percent sign: 100%%\n");

    return 0;
}

scanf() — Formatted Input

scanf() reads formatted input from the keyboard. You must pass the address of the variable using the & operator (except for strings/arrays).

getchar() / putchar() and gets() / puts()

getchar() reads a single character from stdin. putchar() writes a single character to stdout. gets() is unsafe (no bounds checking) — use fgets() instead.

scanf, getchar and putchar

#include <stdio.h>

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

    // scanf reads formatted input; & gives the address of the variable
    printf("Enter your name: ");
    fgets(name, sizeof(name), stdin);  // safer than gets()

    printf("Enter your age: ");
    scanf("%d", &age);

    printf("Enter your salary: ");
    scanf("%f", &salary);

    printf("\nName:   %s", name);
    printf("Age:    %d\n", age);
    printf("Salary: %.2f\n", salary);

    // getchar / putchar — single character I/O
    printf("\nEnter a character: ");
    getchar();  // consume leftover newline from scanf
    char ch = getchar();
    printf("You entered: ");
    putchar(ch);
    putchar('\n');

    // puts — prints string with automatic newline
    puts("Done!");

    return 0;
}

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C Input and Output

printf() — Formatted Output

Escape Sequences

scanf() — Formatted Input

getchar() / putchar() and gets() / puts()

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