Type Conversion (Casting)

Type Conversion (Casting)

Values often need to move between types - an int into a double, a double into an int. That movement is called type conversion.

Implicit conversion

Sometimes C converts types for you, automatically:

int a = 5;
double b = a;      // 5 -> 5.0, no complaint

The narrowing trap

Going the other way can silently lose data:

double pi = 3.99;
int x = pi;        // x becomes 3, the .99 silently disappears

This is narrowing: data is quietly lost.

The integer division trap

Dividing two ints does integer division - the fractional part is thrown away:

int a = 7;
int b = 2;
printf("%d", a / b);   // 3, not 3.5!

Explicit conversion: casting

To convert on purpose, write the target type in parentheses before the value:

int a = 7;
int b = 2;
double result = (double)a / b;   // 3.5

TL;DR

• Implicit conversion happens automatically (int to double is safe).
• Narrowing quietly loses data (double to int drops the fraction).
• Integer division: 7 / 2 is 3, not 3.5.
• Use a cast to convert on purpose: (double)a / b.