math - Addition using printf in C -

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this question has answer here:

on net: using printf add 2 numbers(without using operator) following:

main() {     printf("summ = %d",add(10,20))     return 0; }  int add(int x,int y) {        return printf("%*d%*d",x,' ',y,' '); }

could please explain, how works:

return printf("%*d%*d",x,' ',y,' ');

note: fails when call "sum" following:

sum(1,1) or sum(3,-1)

there 2 central concepts here:

  1. printf() returns number of characters printed.
  2. the %*d format specifier causes printf() read 2 integers arguments, , use first set field width used format second (as decimal number).

so in effect values being added used field widths, , printf() returns sum.

i'm not sure actual d formatting of space character, @ moment. looks weird, have gone empty string instead:

static int sum(unsigned int a, unsigned int b) {     return printf("%*s%*s", a, "", b, ""); }  int main(void) {     unsigned int = 13, b = 6;     int apb = sum(a, b);      printf("%d + %d = %d?\n", a, b, apb);      return 0; }

the above works , computes sum 19.


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