Conversion and Casting

C is statically-typed at compile time. Hence, after a variable is declared, assigning a value of a value of a different type (unless it's implicitly convertible to the target type) to the variable is prohibited. There are several ways to convert types in C.

Implicit conversions

Implicit conversions exist in JavaScript as well as in C (called type coercions). Consider the following example:

let intNumber = 1;
let longNumber = intNumber;

In C:

#include <stdio.h>

int main() {
    int int_number = 1;
    long long_number = int_number; // No error in C
    printf("int_number: %d, long_number: %ld\n", int_number, long_number);
    return 0;
}

By assigning the address of s to t, it is possible to achieve a similar implicit conversion in C:

void bar() {
    const char *s = "hi";
    const char *t = s;
}

See also:

• [Deref coercion]

Explicit conversions

If converting could cause a loss of information, JavaScript requires explicit conversions using a casting expression:

let a = 1.2;
let b = parseInt(a);

C does not handle exceptions during conversions:

#include <stdio.h>

int main() {
    int int_number = 1;
    long long_number = (long)int_number;
    
    // Additional code for demonstration
    printf("Integer: %d\n", int_number);
    printf("Long: %ld\n", long_number);
    
    return 0;
}

Custom conversion

In C, type conversion is typically achieved through explicit casting:

#include <stdio.h>
#include <string.h>

typedef struct {
    char value[100];
} MyId;

void fromMyIdToString(MyId myId, char* result) {
    strcpy(result, myId.value);
}

int main() {
    MyId myId;
    strcpy(myId.value, "id");

    char result[100];
    fromMyIdToString(myId, result);

    printf("%s\n", result);

    return 0;
}