How Do Parameter Modifications Inside a Function Affect the Calling Function in C and C ?

Parameter Modification within Functions: Impact on the Caller

When modifying a parameter within a function, it's crucial to understand its effect on the caller. In the presented code snippet:

<br>void trans(double x,double y,double theta,double m,double n)<br>{</p>
<pre class="brush:php;toolbar:false">m=cos(theta)*x+sin(theta)*y;
n=-sin(theta)*x+cos(theta)*y;

}

calling this function with trans(center_x,center_y,angle,xc,yc) doesn't directly modify the values of xc and yc. This occurs because C passes function parameters by value, meaning the function receives a copy of the variables.

To address this, you have two options:

1. In C :

Use references to pass parameters by reference, modifying the original variables within the function:

<br>void trans(double x, double y, double theta, double& m, double& n)<br>{</p>
<pre class="brush:php;toolbar:false">m=cos(theta)*x+sin(theta)*y;
n=-sin(theta)*x+cos(theta)*y;

}

2. In C:

Pass parameters by explicitly passing their addresses using pointers:

<br>void trans(double x, double y, double theta, double<em> m, double</em> n)<br>{</p>
<pre class="brush:php;toolbar:false">*m=cos(theta)*x+sin(theta)*y;
*n=-sin(theta)*x+cos(theta)*y;

}

With these modifications, calling trans(center_x,center_y,angle,xc,yc) will directly update the values of xc and yc. If this behavior is desired, then using references or pointers is necessary to achieve the desired effect.

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