プログラマ専用SNS ミクプラ

コード:

void
sub
(
int
*
a
)
{
*
a
=
10
;
}
int
main
(
void
)
{
int
n
;
sub
(
&
n
)
;
switch
(
n
)
{
case
0
:
return
1
;
break
;
case
10
:
n
=
0
;
break
;
case
100
:
return
2
;
break
;
default
:
return
3
;
break
;
}
return
n
;
}

コード:

#include <stdio.h>   // fopen, fgets, printf, puts, FILE
#include <stdlib.h>  // strtod
#include <ctype.h>   // isspace

typedef struct {
    unsigned char c;
    const char *p;
} Expr;

const char o[] = "+-*/";

int get(Expr *e)
{
    do e->c = *e->p++; while (isspace(e->c));
    return e->c;
}

double expr(Expr *e, const char *b)
{
    double v;
    if (*b)
        for (v = expr(e, b+2); e->c == b[0] || e->c == b[1]; )
            switch (e->c) {
            case '+': v += expr(e, b+2); break;
            case '-': v -= expr(e, b+2); break;
            case '*': v *= expr(e, b+2); break;
            case '/': v /= expr(e, b+2); break;
            }
    else
        switch (get(e)) {
        case '0': case '1': case '2': case '3': case '4':
        case '5': case '6': case '7': case '8': case '9': case '.':
                  v = strtod(e->p-1, (char**)&e->p); get(e); break;
        case '(': v = expr(e, o); e->c == ')' ? get(e) : (e->c = 1); break;
        case '+': v = expr(e, b); break;
        case '-': v = -expr(e, b); break;
        default:  v = e->c = 1;
        }
    return v;
}

int calc(const char *s, double *v)
{
    Expr e;
    e.p = s;
    *v = expr(&e, o);
    return e.c;
}

int main(int argc, char *argv[])
{
    char buf[4][256];  double v;  FILE *fp = stdin;
    if (argc == 2) {
        fp = fopen(argv[1], "r");
        if (!fp) return 1;
    }
    while (fgets(buf[0], sizeof buf, fp) && buf[0][0] != '.')
        calc(buf[0], &v) ? puts(" error") : printf(" %.15g <== %s", v, buf);
    return 0;
}