What is the easiest way to get an int in a console app?

Question

I want to process user input as an integer, but it seems as though C has no way to get an int from stdin. Is there a function to do this? How would I go about getting an int

Answer 1

Aside from (f)scanf, which has been sufficiently discussed by the other answers, there is also atoi and strtol, for cases when you already have read input into a string but want to convert it into an int or long.

char *line;
scanf("%s", line);

int i = atoi(line);  /* Array of chars TO Integer */

long l = strtol(line, NULL, 10);  /* STRing (base 10) TO Long */
                                  /* base can be between 2 and 36 inclusive */

strtol is recommended because it allows you to determine whether a number was successfully read or not (as opposed to atoi, which has no way to report any error, and will simply return 0 if it given garbage).

char *strs[] = {"not a number", "10 and stuff", "42"};
int i;
for (i = 0; i < sizeof(strs) / sizeof(*strs); i++) {
    char *end;
    long l = strtol(strs[i], &end, 10);
    if (end == line)
        printf("wasn't a number\n");
    else if (end[0] != '\0')
        printf("trailing characters after number %l: %s\n", l, end);
    else
        printf("happy, exact parse of %l\n", l);
}