Is it possible to do multiple operations in increment part of for loop in C/C++?

Question

Is it possible to do multiple operations in increment part of for loop in C/C++? Something like this:

int a = 0, b = 0, c = 5;
for(; a < c; increase a by 1 and increase b by 2)

Answer 1

Use the comma operator:

for (; a < c; ++a, b += 2)

Answer 2

Yes it is possible. You can also declare multiple variables inside the loop and don't need to do it before.

for (int a = 0, b = 0, c = 5; a < c; ++a, b += 2)

Answer 3

@Zoey Hewll's comment:

What about declaring multiple variables of different types?

@AliciaBytes's comment:

multiple declarations in a for loop only works if they are all of the same type.

This might be close to heresy, but you could use a struct to contain multiple variables of different types like this:

#define BENCHMARK(elasped)                                                     \
    for (                                                                      \
        struct { uint8_t done; uint32_t start; } __metadata =                  \
            { 0, systick_get() };                                              \
        !__metadata.done;                                                      \
        ((elasped) = elasped_time(__metadata.start)), __metadata.done = 1      \
    )

---

EDIT: Here's a more complete example

#include <stdint.h>
#include <stdio.h>

volatile uint32_t g_systick = 0; //< Incremented by the system clock somewhere else in the code

uint32_t systick_get(void)
{
    return g_systick;
}

uint32_t elasped_time(uint32_t const start)
{
    uint32_t const now = systick_get();
    return now - start;
}

#define BENCHMARK(elasped)                                                     \
    for (                                                                      \
        struct {                                                               \
            uint8_t done;                                                      \
            uint32_t start;                                                    \
        } __metadata = {0, systick_get()};                                     \
        !__metadata.done;                                                      \
        ((elasped) = elasped_time(__metadata.start)), __metadata.done = 1)

int main(void)
{
    uint32_t time = 0;
    BENCHMARK(time)
    {
        int i = 0; //< Something you want to benchmark
    }
    printf("Time = %d\n", time);
    return 0;
}

Here's how the BENCHMARK() macro looks like when expended (using gcc -E)

int main(void) {
    uint32_t time = 0;
    for (
        struct {
            uint8_t done;
            uint32_t start;
        } __metadata = {0, systick_get()};
        !__metadata.done;
        ((time) = elasped_time(__metadata.start)), __metadata.done = 1)
    {
        int i = 0; //< Something you want to benchmark
    }
    printf("Time = %d\n", time);
    return 0;
}

May Dennis Ritchie forgive us.