Lære Pointers and Functions | Pointers in Arrays and Functions

When you pass a variable to a function in C, you can do so either by value or by reference. Passing by value means the function receives a copy of the variable, so changes inside the function don't affect the original.

void update(int *p) {
    *p = 100;
}

Passing by reference means sending the variable's address using a pointer. This allows the function to directly modify the original variable’s value.

main.c


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#include <stdio.h>

// Function that modifies the value of an integer using a pointer
void setToTen(int *numPtr) {
    *numPtr = 10; // Dereference pointer and assign new value
}

int main() {
    int value = 5;

    printf("Before: %d\n", value);
    setToTen(&value); // Pass address of value to function
    printf("After: %d\n", value);

    return 0;
}

In this example, the function setToTen takes a pointer to an integer as its parameter. Inside the function, the pointer is dereferenced using the * operator, allowing direct access to the memory location of the original variable. By assigning *numPtr = 10;, you update the value stored at that address. In main, the address of value is passed to setToTen using the & operator. As a result, after the function call, the variable value is changed from 5 to 10. This demonstrates how passing a pointer enables a function to modify the original variable, rather than just a local copy.

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Suggested prompts:

Can you show me the full code example for `setToTen` and how it's used in `main`?

Can you explain the difference between passing by value and passing by reference with a simple analogy?

What happens if I pass a variable by value but try to modify it inside the function?

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void update(int *p) {
    *p = 100;
}

Passing by reference means sending the variable's address using a pointer. This allows the function to directly modify the original variable’s value.

main.c


              12345678910111213141516
            
#include <stdio.h>

// Function that modifies the value of an integer using a pointer
void setToTen(int *numPtr) {
    *numPtr = 10; // Dereference pointer and assign new value
}

int main() {
    int value = 5;

    printf("Before: %d\n", value);
    setToTen(&value); // Pass address of value to function
    printf("After: %d\n", value);

    return 0;
}

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Tak for dine kommentarer!

Sektion 2. Kapitel 3