Predict3 of 14 · about 6 min

How big is an int?

C does not promise a size for int. It promises a minimum range, and lets each machine choose. sizeof is how you ask this machine what it actually chose; <limits.h> is how you ask for the smallest and largest value a type can hold.

This practice runtime is a 32-bit machine: char is 1 byte, short 2, int 4, long 4, double 8. The laptop you build the project on is probably 64-bit, where long is usually 8. That difference is exactly why code that assumes a size breaks when it moves.

sizeof produces a size_t, an unsigned type. Printing it with %d is a mismatch — cast it to int, or use %zu.

Example

#include <stdio.h>
#include <limits.h>

int main(void) {
    printf("int is %d bytes, from %d to %d\n", (int)sizeof(int), INT_MIN, INT_MAX);
    return 0;
}

prints: "int is 4 bytes, from -2147483648 to 2147483647\n"

Before you run it

printf("%d\n", (int)sizeof(char) + (int)sizeof(short) + (int)sizeof(int));

On this 32-bit practice machine, what does that print?

Your task

Print one line per type in this exact form, using sizeof for the sizes: char=1 short=2 int=4 long=4 double=8 — but work every number out with sizeof rather than typing it.

·Work the sizes out with sizeof rather than typing the numbers

Stuck?

Explain it

Your project will run this on a 64-bit Linux machine. Which number will probably differ, and why does that matter?

Not graded — this is for you.

Where this goes

Project 2 is this investigation done properly: sizes, ranges, and what happens at the edges. You have just written its first few lines.

#include <stdio.h>

int main(void) {
    printf("char=%d short=%d int=%d long=%d double=%d\n",
           /* fill in five sizeof expressions, each cast to int */
           );
    return 0;
}

Ctrl+Enter checks

This is a teaching runtime for a subset of C, running in your browser on a 32-bit model machine. It reports mistakes a real compiler lets through — reading uninitialised memory, running off an array, signed overflow — and it is not the compiler your project uses.

Press Run to see what your program does, or Check when you think it is right. Everything runs here in your browser.