c - scanf read plus sign with integers but not minus, multiplication or division -

while writing arithmetic expression simplifier, observed odd behavior. recreated problem below:

#include <stdio.h>  int main(void) {     int n, i;     char s[200];      for(i=0;i<2;i++){         if(scanf("%d", &n) == 1)         {             printf("%d\n", n);         } else {             scanf("%s", s);             printf("%s\n", s);         }     }     return 0; } 

if input 5+10 reads 5 in n , 10 in s. but, other sign i.e 5-10 read 5 in n , -10 in s expected output.

my question is: c features caused this? checked on: gcc version 4.8.2 , ideone.

edit

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solved problem char char reading of integers. time. :)

if interested: http://ideone.com/ropyqd

if input 5+10 reads 5 in n , 10 in s. but, other sign i.e 5-10 read 5 in n , -10 in s expected output.

you mistaken, determine changing printf() statements can distinguish 1 generating each output. find program reading 5 n in first iteration of loop, , reading either 10 or -10 n, not s on second iteration.

this happens because %d field descriptor reads optionally signed decimal integer. "optionally signed" means preceded either - negative or + positive. thus, both "+10" , "-10" can scanned via %d field.