C Type Conversion

Type Conversion

Sometimes, you have to convert the value of one data type to another type. This is known as type conversion.

For example, if you try to divide two integers, 5 by 2, you would expect the result to be 2.5. But since we are working with integers (and not floating-point values), the following example will just output 2:

int x = 5;
int y = 2;
int sum = 5 / 2;

printf("%d", sum); // Outputs 2

To get the right result, you need to know how type conversion works.

There are two types of conversion in C:

• Implicit Conversion (automatically)
• Explicit Conversion (manually)

Implicit Conversion

Implicit conversion is done automatically by the compiler when you assign a value of one type to another.

For example, if you assign an int value to a float type:

// Automatic conversion: int to float
float myFloat = 9;

printf("%f", myFloat); // 9.000000

As you can see, the compiler automatically converts the int value 9 to a float value of 9.000000.

This can be risky, as you might lose control over specific values in certain situations.

Especially if it was the other way around - the following example automatically converts the float value 9.99 to an int value of 9:

// Automatic conversion: float to int
int myInt = 9.99;

printf("%d", myInt); // 9

What happened to .99? We might want that data in our program! So be careful. It is important that you know how the compiler work in these situations, to avoid unexpected results.

As another example, if you divide two integers: 5 by 2, you know that the sum is 2.5. And as you know from the beginning of this page, if you store the sum as an integer, the result will only display the number 2. Therefore, it would be better to store the sum as a float or a double, right?

float sum = 5 / 2;

printf("%f", sum); // 2.000000

Why is the result 2.00000 and not 2.5? Well, it is because 5 and 2 are still integers in the division. In this case, you need to manually convert the integer values to floating-point values. (see below).

Explicit Conversion

Explicit conversion is done manually by placing the type in parentheses () in front of the value.

Considering our problem from the example above, we can now get the right result:

// Manual conversion: int to float
float sum = (float) 5 / 2;

printf("%f", sum); // 2.500000

You can also place the type in front of a variable:

int num1 = 5;
int num2 = 2;
float sum = (float) num1 / num2;

printf("%f", sum); // 2.500000

And since you learned about "decimal precision" in the previous chapter, you could make the output even cleaner by removing the extra zeros (if you like):

int num1 = 5;
int num2 = 2;
float sum = (float) num1 / num2;

printf("%.1f", sum); // 2.5

Real-Life Example

Here's a real-life example of data types and type conversion where we create a program to calculate the percentage of a user's score in relation to the maximum score in a game:

// Set the maximum possible score in the game to 500
int maxScore = 500;

// The actual score of the user
int userScore = 423;

/* Calculate the percantage of the user's score in relation to the maximum available score.
Convert userScore to float to make sure that the division is accurate */
float percentage = (float) userScore / maxScore * 100.0;

// Print the percentage
printf("User's percentage is %.2f", percentage);