#include<stdio.h>
#include<ctype.h>
#define SIZE 10
int atoi(char s[]);
int main(int argc, char *argv[])
{
int counter=0;
char s[SIZE];
if (argc!=2) printf("Usage: progname integer\n");
while(*argv[1]) s[counter++]=(*argv[1]++);
printf("Twice Result=%d\n",2*atoi(s));
return 0;
}
int atoi(char s[])
{
int n, i,sign;
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;
}
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