question: creating groups of numbers and name each group and do function on groups

[sanfor]

hello there,..

i am having a universal group,
U[20] = { ... }

int U[20];
for (int i=0;i<20;i++) {
scanf("%d",&U[i]);
}

and inner groups which is included in the U[N].
the user should enter the amount of groups:

int amount;
scanf("%d",&amount);

now the user must name each group with a char letter,..
so i kinda did it as a matrix:

first example for my work:
if the U[20] = {1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17...}
the user enter REAL NUMBERS but the Matrix must contain the boolean value

like for group 'a'
the user enters:
4,5,6,7,17

in the first row in the matrix it must be like this:

0 0 0 1 1 1 1 0 0 0 0 0 0 0 0,.... 1 0 0 0 0...

the cell of common numbers will be 1 and else will be 0.

int list[amount][20];
int flag=1;
char name;

for (int i=0;i<amount;i++) {
     scanf("%c",&name);
     for (int j=0;j<20;j++) {
         scanf("%d",&flag);
         if (flag == 0) { break; }
         else { 
              for (int k=0;k<20;k++) {
                   if (U[k] == flag) {
                        list[name-'a'][j]=1;
                   }
                   else {
                        list[name-'a'][j]=0;
                   }
      }
}

name-'a' : refers to the row of the group .
if name = a
then 'a' - 'a' = 0 and it's the first group
name = b..
'b' - 'a' = 1 .. and it's the second group.


the part that i need help with is the next one
where i have to get a string and run it:

for example if i had 3 groups a , b , c.
the string could be a+b+c .. which is the union of all groups.

char str[80];
scanf("%s",&str);

and the question is .. how can i do a loop that knows where to stop and how to take a part the string and do it group by group..

i need your help
and i am willing to explain again if you didn't understand me

[D_Drmmr]

for example if i had 3 groups a , b , c.
the string could be a+b+c .. which is the union of all groups.

char str[80];
scanf("%s",&str);

and the question is .. how can i do a loop that knows where to stop and how to take a part the string and do it group by group..

Well in the specific example you describe, it's easy to parse the string. However, if the syntax of the user input is more complex, it may be worthwhile to build a parser for it.

char str[80];
scanf("%s", &str);
char* p = str;
while (*p) { // while not at end of string
    char c = *p;
    if (!isalpha(c)) {
        // error
    }
    // do operator for group c
    ++p;
    if (*p) { // not at end of string
        if (*p == '+') {
            ++p;
        }
        else {
            // error
        }
    }
}