我正在尝试解决第2版“C编程语言”中的练习2-1,其中要求：
“编写一个程序来确定char,short,int和long变量的范围,包括有符号和无符号,通过从标准头文件中打印适当的值并直接计算.如果你计算它们会更难：确定各种浮动的范围 – 点类型.“
我已经设法确定除浮点之外的所有类型的范围,通过使用标准头中的最小值和最大值以及直接计算.
如何使用直接计算确定浮点类型的范围？
#include <stdio.h>
#include <limits.h>
#include <float.h>
#define TESTBIT 2
/* write a program to determine the ranges of char,int,and long variables,both signed and unsigned by printing appropriate values from standard headers
and by direct computation
harder if you compute them - determine the ranges of the varIoUs floating-point types */
main()
{
char ch,chtest;
unsigned char uch;
short sh,shtest;
unsigned short ush;
int i,itest;
unsigned int ui;
long l,ltest;
unsigned long ul;
long long ll,lltest;
unsigned long long ull;
ch = uch = sh = ush = i = ui = l = ul = ll = ull = 0;
++ch; /* Maximum and minimum ranges using direct computation */
chtest = 0;
while (chtest >= 0) {
chtest = ch * TESTBIT;
if (chtest > 0)
ch = ch * TESTBIT;
}
ch = ch * 2;
printf("Minimum range of signed char variable: %d\n",ch);
--ch;
printf("Maximum range of signed char variable: %d\n",ch);
--uch;
printf("Maximum range of unsigned char variable: %u\n",uch);
++sh;
shtest = 0;
while (shtest >= 0) {
shtest = sh * TESTBIT;
if (shtest > 0)
sh = sh * TESTBIT;
}
sh = sh * 2;
printf("Minimum range of signed short variable: %d\n",sh);
--sh;
printf("Maximum range of signed short variable: %d\n",sh);
--ush;
printf("Maximum range of unsigned short variable: %u\n",ush);
++i;
itest = 0;
while (itest >= 0) {
itest = i * TESTBIT;
if (itest > 0)
i = i * TESTBIT;
}
i = i * 2;
printf("Minimum range of signed int variable: %d\n",i);
--i;
printf("Maximum range of signed int variable: %d\n",i);
--ui;
printf("Maximum range of unsigned int variable: %u\n",ui);
++l;
ltest = 0;
while (ltest >= 0) {
ltest = l * TESTBIT;
if (ltest > 0)
l = l * TESTBIT;
}
l = l * 2;
printf("Minimum range of signed long variable: %d\n",l);
--l;
printf("Maximum range of signed long variable: %d\n",l);
--ul;
printf("Maximum range of unsigned long variable: %lu\n",ul);
++ll;
lltest = 0;
while (lltest >= 0) {
lltest = ll * TESTBIT;
if (lltest > 0)
ll = ll * TESTBIT;
}
ll = ll * 2;
printf("Minimum range of signed long long variable: %lld\n",ll);
--ll;
printf("Maximum range of signed long long variable: %lld\n",ll);
--ull;
printf("Maximum range of unsigned long long variable: %llu\n",ull);
printf("\nSize of char: %d\n",CHAR_BIT); /* Max and min ranges using limits.h and float.h header */
printf("Minimum range of signed char variable: %d\n",SCHAR_MIN);
printf("Maximum range of signed char variable: %d\n",SCHAR_MAX);
printf("Maximum range of unsigned char variable: %u\n",UCHAR_MAX);
printf("Minimum range of signed short variable: %d\n",SHRT_MIN);
printf("Maximum range of signed short variable: %d\n",SHRT_MAX);
printf("Maximum range of unsigned short variable: %u\n",USHRT_MAX);
printf("Minimum range of int variable: %d\n",INT_MIN);
printf("Maximum range of int variable: %d\n",INT_MAX);
printf("Maximum range of unsigned int variable: %u\n",UINT_MAX);
printf("Minimum range of signed long variable: %ld\n",LONG_MIN);
printf("Maximum range of signed long variable: %ld\n",LONG_MAX);
printf("Maximum range of unsigned long variable: %lu\n",ULONG_MAX);
printf("Minimum range of long long variable: %lld\n",LLONG_MIN);
printf("Maximum range of long long variable: %lld\n",LLONG_MAX);
printf("Maximum range of unsigned long long variable: %llu\n\n",ULONG_LONG_MAX);
printf("Minimum range of float variable: %f\n",FLT_MIN);
printf("Maximum range of float variable: %f\n",FLT_MAX);
printf("Minimum range of double variable: %f\n",DBL_MIN);
printf("Maximum range of double variable: %f\n",DBL_MAX);
printf("Minimum range of long double variable: %lf\n",LDBL_MIN);
printf("Maximum range of long double variable: %lf\n",LDBL_MAX);
return 0;
}
解决方法
#include <stdio.h>
main()
{
float fl,fltest,last;
double dbl,dbltest,dblast;
fl = 0.0;
fltest = 0.0;
while (fl == 0.0) {
last = fltest;
fltest = fltest + 1111e28;
fl = (fl + fltest) - fltest;
}
printf("Maximum range of float variable: %e\n",last);
dbl = 0.0;
dbltest = 0.0;
while (dbl == 0.0) {
dblast = dbltest;
dbltest = dbltest + 1111e297;
dbl = (dbl + dbltest) - dbltest;
}
printf("Maximum range of double variable: %e\n",dblast);
return 0;
}