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Parameter Passing Techniques in C

abhinay1111 profile image abhinay1111 ・2 min read

There are different ways in which parameter data can be passed into and out of methods and functions. Let us assume that a function B() is called from another function A(). In this case A is called the “caller function” and B is called the “called function or callee function”. Also, the arguments which A sends to B are called actual arguments and the parameters of B are called formal arguments.
Pass By Value : This method uses in-mode semantics. Changes made to formal parameter do not get transmitted back to the caller. Any modifications to the formal parameter variable inside the called function or method affect only the separate storage location and will not be reflected in the actual parameter in the calling environment. This method is also called as call by value.
// C program to illustrate
// call by value

include

void func(int a, int b)
{
a += b;
printf("In func, a = %d b = %d\n", a, b);
}
int main(void)
{
int x = 5, y = 7;

// Passing parameters
func(x, y);
printf("In main, x = %d y = %d\n", x, y);
return 0;
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}

Pass by reference(aliasing) : This technique uses in/out-mode semantics. Changes made to formal parameter do get transmitted back to the caller through parameter passing. Any changes to the formal parameter are reflected in the actual parameter in the calling environment as formal parameter receives a reference (or pointer) to the actual data. This method is also called as call by reference. This method is efficient in both time and space.
// C program to illustrate
// call by reference

include

void swapnum(int* i, int* j)
{
int temp = *i;
*i = *j;
*j = temp;
}

int main(void)
{
int a = 10, b = 20;

// passing parameters
swapnum(&a, &b);

printf("a is %d and b is %d\n", a, b);
return 0;
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}

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