Input and output statement

 In C, we mainly use these standard library functions (from ) for input and output:

Task	Function	Used for	Notes / Common mistakes
Output (screen)	printf()	formatted output	-most commonly used
Output (screen)	puts()	simple string + newline	-faster than printf for plain text
Output (screen)	putchar()	single character	-rarely used directly
Input (keyboard)	scanf()	formatted input	-needs & for most types (very important!)
Input (keyboard)	getchar()	single character	-returns int (EOF or character)
Input (keyboard)	gets()	whole line (string)	-dangerous – never use (buffer overflow)
Input (safer)	fgets()	whole line (recommended)-	-modern & safe choice

1. Most Important Output Function: printf()

#include <stdio.h> int main() { int age = 21; float marks = 89.75; char grade = 'A'; char name[] = "Pentas"; // Basic printing printf("Hello World\n"); // Printing with variables (format specifiers) printf("My name is %s\n", name); // string printf("I am %d years old\n", age); // integer printf("Marks = %.2f\n", marks); // float → 2 decimal places printf("Grade = %c\n", grade); // single character // Multiple values in one line printf("Name: %s, Age: %d, Marks: %.1f, Grade: %c\n", name, age, marks, grade); return 0; }

2. Most Important Input Function: scanf()

#include <stdio.h> int main() { int roll; float percentage; char section; char firstName[30]; printf("Enter your roll number: "); scanf("%d", &roll); // ← note the & printf("Enter your percentage: "); scanf("%f", &percentage); printf("Enter your section (A/B/C): "); scanf(" %c", &section); // ← space before %c is very important! printf("Enter your first name: "); scanf("%s", firstName); // ← NO & for arrays/strings printf("\nYou entered:\n"); printf("Roll : %d\n", roll); printf("Percentage: %.2f%%\n", percentage); printf("Section : %c\n", section); printf("Name : %s\n", firstName); return 0; }

Very important rules for scanf():

• Use & before variable name for all basic types (int, float, char, double, etc.)
• Do NOT use & for arrays and strings (char name[50])
• Add a space before %c → scanf(" %c", &ch); (otherwise it often reads leftover Enter key \n)

3. Safer Way to Read a Line 

scanf("%s") stops at a space—so "Pentas Hub" becomes only "Pentas". Better to use fgets():

#include <stdio.h> #include <string.h> int main() { char fullName[100]; printf("Enter your full name: "); fgets(fullName, sizeof(fullName), stdin); // Remove trailing newline (very common step) fullName[strcspn(fullName, "\n")] = '\0'; printf("Hello, %s!\n", fullName); return 0; }

You want to read	Best choice today	Alternative (still okay)	Avoid completely
One number	scanf("%d", &x)	—	—
One word (no space)	scanf("%s", name)	—	—
Full name/sentence	fgets()	—	gets()
Single character	scanf(" %c", &ch)	getchar()	—
Just print one line	puts("text")	printf("text\n")	—
Formatted output	printf()	—	—

Mini Practice Program

#include <stdio.h>

int main()

{

    char name[50];

    int age;

    float height;

    printf("Enter your name     : ");

    fgets(name, sizeof(name), stdin);

    name[strcspn(name, "\n")] = '\0';

    printf("Enter your age      : ");

    scanf("%d", &age);

    printf("Enter your height (cm): ");

    scanf("%f", &height);

    printf("\n--- Your Details ---\n");

    printf("Name   : %s\n", name);

    printf("Age    : %d years\n", age);

    printf("Height : %.1f cm\n", height);

    return 0;

}

Common format specifiers: