Input and Output in C

C handles I/O through the stdio.h (Standard Input/Output) library.

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printf() — Formatted Output

printf("format string", arg1, arg2, ...);

Format specifiers:

Escape sequences:

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scanf() — Formatted Input

scanf("format string", &var1, &var2, ...);

Note: Always use the address-of operator & with scanf (except for strings).

Example:

#include <stdio.h>

int main() {
    int age;
    float height;
    char name[50];
    
    printf("Enter age: ");
    scanf("%d", &age);
    
    printf("Enter height: ");
    scanf("%f", &height);
    
    printf("Enter name: ");
    scanf("%s", name);   /* no & for arrays */
    
    printf("Name: %s, Age: %d, Height: %.2f\n", name, age, height);
    return 0;
}

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Character I/O

char c;
c = getchar();     /* reads one character */
putchar(c);        /* prints one character */

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String I/O

char str[100];
gets(str);           /* reads a line (unsafe — do not use in production) */
puts(str);           /* prints string + newline */
fgets(str, 100, stdin);  /* safe alternative to gets */

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Complete Example

#include <stdio.h>

int main() {
    int a, b, sum;
    
    printf("Enter two integers: ");
    scanf("%d %d", &a, &b);
    
    sum = a + b;
    printf("Sum = %d\n", sum);
    
    return 0;
}