Check if a string has only numbers in C?

Question

I\'m trying to write a simple code to check if a string only has numbers in it. So far it\'s not working, any help would be appreciated.

#include          


        

Answer 1

You might consider using strspn:

#include 
#include 

int main(int argc, char* argv[]) {
    int i;
    for (i=1; i < argc; i++) {
        printf("%s %s\n",
            strlen(argv[i]) == strspn(argv[i], "0123456789") ? "digits" : "mixed",
            argv[i]
        );
    }
}

Demoed:

$ ./try foo 123 ba23a 123.4
mixed foo
digits 123
mixed ba23a
mixed 123.4

strspn returns the initial number of characters from the first argument that appear in the second argument. Super simple examples:

strspn("abba", "a");  // == 1
strspn("abba", "b");  // == 0
strspn("abba", "ab"); // == 2