#include <stdio.h>

void tres_somas(float *a, float *b, float *c);

int main()
{
    float a = 5, b = 6, c = 7;

    tres_somas(&a, &b, &c);
    printf("a = %.1f, b = %.1f, c = %.1f\n", a, b, c);
    
    return 0;
}

void tres_somas(float *a, float *b, float *c)
{
     float sa = *b + *c;
     float sb = *a + *c;
     float sc = *a + *b;
     *a = sa;
     *b = sb;
     *c = sc;
}