K&R atoi-general memory leak

Question

I am following K&R second edition examples to learn C and coding as I think this is correct way of doing things. Anyhow when I run this program post compilation the program get stuck. I used valgrind for execution of compiled script.

#include <ctype.h>

int atoi(char s[])
{
    int i, n, sign;
    for(i = 0; isspace(s[i]); i++)
        ;
    sign = (s[i] == '-')? -1 : 1;
    if (s[i] == '+'|| s[i] == '-')
        i++;
    for (int n = 0; isdigit(s[i]); n++)
        n = 10 * n + (s[i]-'0');
    return sign * n;
}

int main()
{
    char input[] = "       -12345";
    atoi(input);
}
# vaibhavchauhan at startup001 in ~/Documents/Projects/K-R on git:master x [0:43:36]
$ valgrind ./atoi-general
==8075== Memcheck, a memory error detector
==8075== Copyright (C) 2002-2015, and GNU GPL'd, by Julian Seward et al.
==8075== Using Valgrind-3.11.0 and LibVEX; rerun with -h for copyright info
==8075== Command: ./atoi-general
==8075==
^C==8075==

Answer 1

In your second loop, you are iterating n but you use i for your computations and computations. This leads to the infinite loop you observe. To fix this, use either i as an index consistently:

int atoi(char s[])
{
    int i, sign, n;
    for(i = 0; isspace(s[i]); i++)
        ;
    sign = (s[i] == '-')? -1 : 1;
    if (s[i] == '+'|| s[i] == '-')
        i++;
    for (n = 0; isdigit(s[i]); i++)
        n = 10 * n + (s[i]-'0');
    return sign * n;
}

Note that indices should have type size_t, not int as the latter might be not large enough to index every array. For this purpose, an index of type int is fine though.