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atof-pointer.c
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atof-pointer.c
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#include <stdio.h>
#include <ctype.h>
#include <assert.h>
/* atof:convert string s to double */
double atof(const char *s);
double atof(const char *s)
{
double val, power, exponent, exponent_modifier, base_and_exponent;
int sign;
/* skip white space */
while (isspace(*s)) {
s++;
}
sign=(*s == '-') ? -1 : 1;
if (*s == '+' || *s == '-') {
s++;
}
for (val = 0.0; isdigit(*s); s++) {
val = 10.0 * val + (*s - '0');
}
if (*s == '.') {
s++;
}
for (power = 1.0; isdigit(*s); s++) {
val = 10.0 * val + (*s - '0');
power *= 10;
}
base_and_exponent = 1;
if (*s == 'e') {
s++;
exponent = atof(s);
if (exponent < 0) {
exponent_modifier = 0.1;
exponent = - exponent;
} else {
exponent_modifier = 10;
}
/* printf("Exponent: %f\n", exponent); */
for(int j = 0; j < exponent; j++) {
base_and_exponent *= exponent_modifier;
/* printf("base and mod: %f\n", base_and_exponent); */
}
}
return sign * val * base_and_exponent/ power;
}
void test_atof(const char *s, double expected)
{
double result = atof(s);
printf("%25f\n%25f\n\n", expected, result);
/* comparing floats is non-trivial, eyeball it. */
/* assert(expected == result); */
}
int main()
{
printf("Done!\n");
test_atof("0",0);
test_atof("1", 1);
test_atof("-1", -1);
test_atof("-123", -123);
test_atof("3.14", 3.14);
test_atof("123.45", 123.45);
test_atof("123.45e6", 123.45e6);
test_atof("123.45e-2", 123.45e-2);
test_atof("123.45e-6", 123.45e-6);
}