How Do C and C Functions Handle Parameter Modifications?

Functions in C : Parameter Modifications

Passing parameters into functions can raise questions regarding their behavior once inside. Parameters can take different forms depending on the programming language, and in C , there are two main options.

When you declare a function as follows:

void trans(double x, double y, double theta, double m, double n)

the parameters x, y, theta, m, and n are passed by value (i.e., their copies are created inside the function). Any changes made to these parameters within the function will not affect the original values in the caller.

To modify the actual values in the caller, you can utilize references instead. By using a reference, the parameter becomes an alias for the variable in the calling function.

void trans(double x, double y, double theta, double& m, double& n)
{
    // Modifications to m and n will affect the caller's variables
}

When invoking the trans function using references:

trans(center_x, center_y, angle, xc, yc);

the values of xc and yc in the calling function will be updated with the changes made within trans.

In C, a slightly different approach is required. Instead of references, you would need to pass explicit pointers or addresses to the variables that should be modified. Here's an example:

void trans(double x, double y, double theta, double* m, double* n)
{
    // Modifications via pointer indirection (e.g., *m) will update the caller's variables
}

// In main:
trans(center_x, center_y, angle, &xc, &yc);

The & operator allows you to pass the address of the variable, enabling the function to access and modify the actual value.

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