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#include <stdio.h>
static int is_digit(char character)
{
return character >= '0' && character <= '9';
}
int main(void)
{
printf("calc, e.g. 3 + 4 * 2 (left to right), empty line quits\n");
char line[128];
for (;;)
{
printf("> ");
int length = readline(line, 128);
printf("\n");
if (length == 0)
break;
long accumulator = 0;
char operator = '+';
int valid = 1;
int saw_number = 0;
int position = 0;
while (position < length)
{
char character = line[position];
if (character == ' ')
{
position++;
continue;
}
if (is_digit(character))
{
long value = 0;
while (position < length && is_digit(line[position]))
value = value * 10 + (line[position++] - '0');
if (operator == '+')
accumulator += value;
else if (operator == '-')
accumulator -= value;
else if (operator == '*')
accumulator *= value;
else if (operator == '/' || operator == '%')
{
if (value == 0)
{
printf("divide by zero\n");
valid = 0;
break;
}
accumulator = (operator == '/') ? accumulator / value : accumulator % value;
}
saw_number = 1;
}
else if (character == '+' || character == '-' || character == '*'
|| character == '/' || character == '%')
{
operator = character;
position++;
}
else
{
printf("bad character\n");
valid = 0;
break;
}
}
if (valid && saw_number)
printf("= %ld\n", accumulator);
}
return 0;
}
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