Question

I have a problem with sscanf() in the following code:

void num_check(const char*ps){
char *ps1=NULL;
int number=0;
unsigned sum_num=0;
ps1=ps;

for(;*ps1!='\0';ps1++){
    if (isdigit(*ps1)){
      sscanf(ps1,"%d",&number);
      sum_num+=number;
    }
    }
printf("Sum of digits is: %d",sum_num);


}


int main(){

printf("Enter a string:\n");
char str[20];
gets(str);
num_check(str);
return 0;
}

The problem is: when I input a string in the form of “w2b4e” it sums my numbers OK, and I get the desired result. But when I try to input a string such as “w23b4e”, what it does is: it sees the number 23 in the loop, so variable number=23, and sum_num=23, but the next step in the loop is this: number=3, and sum_num=26. And in the next step sum_num= 30…
This confuses me quite a bit. Since I don’t believe that sscanf() has such a quirky flaw, what am I doing wrong?

Answer 1

If you want to sum digits (not the whole number), use the following instead:

if( isdigit(*ps1)) {
  sum_num += *ps1 - '0';
}

You can also use sscanf("%1d", ps1) to make it read only one character.