Data types (signed and unsigned): Numeric (int, short int, long, float, double), Character (char, string), void

📖 Theory

Three values, three shaped boxes

The marks program is growing and today it must store three things: marks 78, percentage 78.5, and grade 'A'.

Try pouring all three into int boxes and watch: 78 fits perfectly, 78.5 loses its .5, and 'A' becomes a number you never asked for.

Boxes have shapes. Choosing the shape is what a data type does, and choosing wrong is the quietest way for a C program to lie to you.

📖 Theory

The dabba set

A kitchen dabba set has shapes for a reason: a flat one for rotis, a tall one for dal, a tiny one for elaichi. Pour dal into the roti box and you lose half of it. Data types are the shapes: int for whole numbers, float/double for values with decimals, char for a single character. The type also fixes the box's SIZE in bytes, which decides how big a value can fit.

📊 At a glance

The C type family (typical sizes)

📖 Theory

The special ones: string, void, signed/unsigned

• string: NOT a basic C type. Text like "Riya" is a char array, a row of char boxes, written in double quotes. Full treatment comes in Unit 3; for now, know why 'A' and "A" differ.
• void: the "no value" type, used for functions that return nothing. No variable is declared void.
• signed / unsigned: in a signed int, one bit stores the sign, leaving ~±214 crore. Declare unsigned int and that bit joins the value: no negatives, double the positive reach (~429 crore). Perfect for counts that can never be negative.

⌨️ Practical

The marks program, properly typed

#include <stdio.h>

int main() {
    int marks = 78;
    float percentage = 78.5;
    char grade = 'A';
    unsigned int total_students = 60;

    printf("Marks: %d\n", marks);
    printf("Percentage: %f\n", percentage);
    printf("Grade: %c\n", grade);
    return 0;
}

This example runs in Gri-Learn on the web, where you can edit it and see the output.

🧩 Quiz

You declare int percentage = 78.5; What does the box actually hold?

1. 78, the decimal part is cut off
2. 78.5, C adjusts the box automatically
3. 79, C rounds to the nearest whole number
4. 0, the program refuses the value

💭 Think first

The char secret you already know

A char box is 1 byte, and bytes hold numbers. So what number sits in the box when you store 'A'? You learned this in BCA103.

⚠️ Watch out

Where marks leak

Calling string a basic data type of C: it is a char array, and examiners check. Writing sizes as universal laws: they are typical (int is "usually 4 bytes", compiler-dependent), say so. Quoting wrong: 'A' is a char, "A" is a string of two bytes (A plus a hidden end-marker). And unsigned does not mean "no sign written": it means negatives are impossible for that box.

📖 Theory

Choosing like a professional

The working rule: whole counts → int (unsigned if negatives are impossible), money and percentages → float, science-grade precision → double, one letter/symbol → char. Get the shapes right now, because the next lesson hands you the verbs, operators, and 78 / 60 behaves very differently in int boxes versus float boxes.

✅ Summary

Key takeaways

• A data type fixes a box's size (bytes) and what values fit.
• Whole numbers: short int, int, long; decimals: float (~7 digits), double (~15).
• char holds ONE character, stored as its ASCII number; 'A' is 65.
• string is a char array (double quotes), not a basic type; void means no value.
• unsigned sacrifices negatives to double the positive range.
• int boxes truncate decimals: 78.5 becomes 78, no rounding.
• Memory hook: the dabba set, right shape for the right thing.