C语言中比较好的方法

/*删除一个字符串中相同的字符*/
# include <stdio.h>

int main()
{
char s[27];
gets(s);
int i, j, k;

for (i=0; i<26; i++)
{
for (j=k=i+1; j<26; j++)
{
if (s[i] != s[j])
s[k++] = s[j];
}

s[k] = '\0';
}

puts(s);

return 0;
}

/*对一个数组不断的写入，然后返回值存放在一个指向指针的指针数组里面*/
# include <stdio.h>
# include <string.h>
# include <malloc.h>

int main()
{
char s[10];
int i;

char *ss[10];

for (i=0; i<10; i++)
{
gets(s);
ss[i] = strdup(s);
}

for (i=0; i<10; i++)
{
printf("%s\n", ss[i]);
}

return 0;
}

char *strdup(char *string)
{
char *new_string;

new_string = (char *)malloc(strlen(string) + 1);

if (new_string == NULL)
strcpy(new_string, string
4000
);

return new_string;
}

删除字符之间多余的空格
# include <stdio.h>

int main()
{
int c, lastc;
lastc = ' ';

while ((c = getchar()) != EOF)
{
if (c != ' ')
putchar(c);
else if (lastc != ' ')
putchar(c);

lastc = c;
}

return 0;
}

以每行一个单词输出
# include <stdio.h>

int main()
{
int c, state;

state = 0;
while ((c = getchar()) != EOF)
{
if (c == ' ' || c == '\n' || c == '\t')
{
if (state == 1)
{
putchar('\n');
state = 0;
}
}
else if (state == 0)
{
state = 1;
putchar(c);
}
else
{
putchar(c);
}
}

return 0;
}

# include <stdio.h>
# include <string.h>
# include <malloc.h>
# include <stdlib.h>
# define N 100

void print_tokens(char *s);

int main()
{
char s
;
gets(s);

print_tokens(s);

return 0;
}

void print_tokens(char *s)
{
int count = 0;
char white[] = " \n\t\f\v\r";
char *token;

for (token=strtok(s, white); token != NULL; token=strtok(NULL, white))
{
count++;
puts(token);
}

printf("%d\n", count);
}

统计各个字符出现的次数
# include <stdio.h>
# include <ctype.h>
# define MAXCHAR 128

int main()
{
int c, i;
int cc[MAXCHAR] = {0};

while ((c = getchar()) != EOF)
{
if (c < MAXCHAR)
++cc[c];					//在数组中对应的位置上自增 最后输出该数即可
}

for (i=1; i<MAXCHAR; i++)
{
if (isprint(i))
printf("%5d-%c-%5d : ", i, i, cc[i]);
else
printf("%5d--%5d : ", i, cc[i]);
}

return 0;
}

字符数组转16进制
# include <stdio.h>
# define YES 1
# define NO 0

int htoi(char *s);

int main()
{
int n;
char s[100];
gets(s);

n = htoi(s);

printf("%d\n", n);

return 0;
}

int htoi(char *s)
{
int hexdigit, i , inhex, n;

i = 0;
if (s[i] == '0')
{
i++;
if (s[i] == 'x' || s[i] == 'X')
i++;
}

n = 0;
inhex = YES;
for ( ; inhex == YES; ++i)
{
if (s[i] >= '0' && s[i] <= '9')
hexdigit = s[i] - '0';
else if (s[i] >= 'a' && s[i] <= 'f')
hexdigit = s[i] - 'a' + 10;
else if (s[i] >= 'A' && s[i] <= 'F')
hexdigit = s[i] - 'A' + 10;
else
inhex = NO;

if (inhex == YES)
n = 16 * n + hexdigit;
}

return n;
}

从字符串s1中删除字符串s2中出现的字符
（不用标记的方法）
# include <stdio.h>
# define N 100

void squeeze(char *s1, char *s2);

int main()
{
char s1
;
char s2
;

gets(s1);
gets(s2);

squeeze(s1, s2);

puts(s1);

return 0;
}

void squeeze(char *s1, char *s2)
{
int i, j, k;

for (i=k=0; s1[i] != '\0'; i++)
{
for (j=0; s2[j] != '\0' && s2[j] != s1[i]; j++)
;

if (s2[j] == '\0')
s1[k++] = s1[i];
}

s1[k] = '\0';
}

在s1中匹配s2的字符串
# include <stdio.h>
# define MAXLINE 1000

int getline(char s[], int lim);
int strindex(char s[], char t[]);

char pattern[] = "ould";

int main()
{
char line[MAXLINE];
int found = 0;

while (getline(line, MAXLINE) > 0)
if (strindex(line, pattern) >= 0)
{
printf("%s\n", line);
found++;
}

return found;
}

int getline(char s[], int lim)
{
int c, i;

i = 0;
while (--lim > 0 && (c = getchar()) != EOF && c != '\n')
s[i++] = c;
if (c == '\n')
s[i++] = c;
s[i] = '\0';

return i;

int strindex(char s[], char t[])
{
int i, j, k;

for (i=0; s[i] != '\0'; i++)
{
for (j=i, k=0; t[k] != '\0' && s[j] == t[k]; j++, k++)
;
if (k > 0 && t[k] == '\0')
return i;
}

return -1;
}

科学计数法转十进制
# include <stdio.h>
# include <ctype.h>

double atof(char s[]);

int main()
{
double value;
char s[10];
printf("请输入你需要转换的科学表示法:\n");
gets(s);

value = atof(s);

printf("%lf\n", value);

return 0;
}

double atof(char s[])
{
double val, power;
int exp, i, sign;

for (i=0; isspace(s[i]); i++)
;

sign = (s[i] == '-') ? -1 : 1;
if (s[i] == '+' || s[i] == '-')
i++;
for (val = 0.0; isdigit(s[i]); i++)
val = 10.0 * val + (s[i] - '0');
if (s[i] == '.')
i++;
for (power=1.0; isdigit(s[i]); i++)
{
val = 10.0 * val + (s[i] - '0');
power *= 10.0;
}

val = sign * val / power;

if (s[i] == 'e' || s[i] == 'E')
{
sign = (s[++i] == '-') ? -1 : 1;

if (s[i] == '+' || s[i] == '-')
i++;
for (exp=0; isdigit(s[i]); i++)
exp = 10 * exp + (s[i] - '0');
if (sign == 1)
while (exp-- > 0)
val *= 10;
else
while (exp-- > 0)
val /= 10;
}

return val;
}

递归将数字转化成字符串
# include <stdio.h>

void fun(int a);

int main()
{
int a;
scanf("%d", &a);

fun(a);

return 0;
}

void fun(int a)
{
if (a < 0)
{
putchar('-');
a = -a;
}

if (a / 10)
fun(a / 10);
putchar(a % 10 + '0');

}

检测s1的后边是不是字符串s2
# include <stdio.h>
# define N 100

bool strend(char *s1, char *s2);

int main()
{
char s1
;
char s2
;

gets(s1);
gets(s2);

if ( strend(s1, s2) )
printf("YES\n");
else
printf("NO\n");

return 0;
}

bool strend(char *s1, char *s2)
{
char *ps1 = s1;
char *ps2 = s2;

while (*s1)
s1++;
while (*s2)
s2++;

for ( ; *s1 == *s2; s1--, s2--)
if (s1 == ps1 || s2 == ps2)
break;

if (*s1 == *s2 && s2 == ps2 && *s1 != '\0')
return true;
else
return false;
}