Type Conversion & Casting in C

What is Type Conversion?

Type conversion happens when a value of one data type is used in a context that requires another data type.

Types of Type Conversion

1. Implicit Type Conversion (Automatic)
2. Explicit Type Conversion (Casting)

1. Implicit Type Conversion (Automatic)

The compiler performs this conversion itself.

Conversion Rules

• char → int → float → double
• Smaller type converts to larger type
• No data-loss if converting upward

Example – Implicit Conversion

#include <stdio.h>

int main() {

    int a = 10;
    float b = a;   // int → float

    printf("a = %d\n", a);
    printf("b = %.2f\n", b);

    return 0;
}

Example – Automatic Type Promotion in Expressions

#include <stdio.h>

int main() {

    int a = 5;
    float b = 2.5;

    float result = a + b;   // int → float

    printf("Result = %.2f", result);

    return 0;
}

2. Explicit Type Conversion (Casting)

Casting is done manually by the programmer using a cast operator: (data_type)

Example – Explicit Casting

#include <stdio.h>

int main() {

    float x = 10.75;

    int y = (int)x;   // casting float → int

    printf("x = %.2f\n", x);
    printf("y = %d\n", y);

    return 0;
}

Output:

10.75 → 10 (decimal removed)

Difference Between Implicit & Explicit Conversion

Implicit (automatic):
- Performed by compiler
- No syntax needed
- Safe when converting smaller to larger

Explicit (casting):
- Forced by programmer
- Syntax required: (int), (float)
- Risk of data loss

Example – Preventing Wrong Division

#include <stdio.h>

int main() {

    int a = 5, b = 2;

    float result1 = a / b;            // integer division → 2
    float result2 = (float)a / b;     // correct float division → 2.5

    printf("Without casting: %.2f\n", result1);
    printf("With casting: %.2f\n", result2);

    return 0;
}

Example – Casting in Expressions

#include <stdio.h>

int main() {

    int x = 7, y = 3;

    float div = (float)(x + y) / 2;

    printf("Average = %.2f", div);

    return 0;
}

Example – char to int Conversion

#include <stdio.h>

int main() {

    char ch = 'A';

    int ascii = (int)ch;

    printf("ASCII of A = %d", ascii);

    return 0;
}

Common Mistakes

• Forgetting to add parentheses in casting
• Casting after division instead of before
• Thinking casting changes original variable (it doesn’t)

Practice Questions

1. What is implicit type conversion? Give two examples.
2. Explain explicit type casting with syntax.
3. What happens when float is cast to int?
4. Write a program to convert char to ASCII number.
5. Why is casting important in division?

Practice Task