1.字符串拷貝
2.串比較
3.字符替換
4.字符串順序
5.轉換成double
6.轉大寫
7.刪除

#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

//字符串拷貝
/*
int main(){
char s[] = "Golden Global View";
//默認值
char d[5];

strcpy(d, s);
//d[4] = '\0';
printf("%s\n", d);

getchar();

return 0;
}
*/

/*
//串比較
int main(){
char *p1 = "ABC";
char *p2 = "abc";

int r = strcmp(p1, p2);
if (r > 0){
printf("p1>p2");
}
else if (r == 0){
printf("p1=p2");
}
else{
printf("p1<p2");
}
printf("\n\n");

getchar();

return 0;
}
*/


//字符替換
//_strset:將所有的字符都換掉
/*
void main(){
char p1[] = "ABC CBA NBA";
_strset(p1, 'C');
printf("%s", p1);
getchar();
}
*/


//字符串順序
//strrev:將字符串倒序排列
/*
void main(){
char p1[] = "ABC CBA NBA";
_strrev(p1);
printf("%s", p1);
getchar();
}
*/


//類型轉換：字符轉成int、double等等......
/*
void main(){
char p1[] = "10A0";
//轉成int類型
int r = atoi(p1);
//轉成double類型
float rd = atof(p1);



printf("%d\n", r);
printf("%f", rd);
getchar();
}
*/


//轉換成double
/*
void main(){
char *p1 = "12A5";
char ** p2 = &p1;
//轉成double類型
double rd = strtod(p1,p2);
printf("%f\n", rd);
printf("%c", **p2);
getchar();
}
*/


//字符大小轉換(大寫轉小寫，小寫轉大寫)
//轉大寫
/*
void charToUpper(char c[],int len){
int i = 0;
for (; i < len; i++){
//其實本質就是判斷處理ASCII
if (c[i] >= 'a' && c[i] <= 'z'){
//假設：
//a->ASCII:61
//c[i] = 'c' ->  ASCII:63(十進制)
//以上公式等價于：C = 63 - 61 + 41
//A->ASCII:41
//C->ASCII:43

c[i] = c[i] - 'a' + 'A';
}
}
}

//轉大寫
void charToLower(char c[], int len){
int i = 0;
for (; i < len; i++){
//其實本質就是判斷處理ASCII
if (c[i] >= 'A' && c[i] <= 'Z'){
c[i] = c[i] - 'A' + 'a';
}
}
}

void main(){
char p1[] = "abcd";
charToUpper(p1, strlen(p1));
printf("轉大寫：%s\n", p1);
charToLower(p1, strlen(p1));
printf("轉小寫：%s\n", p1);
getchar();
}
*/

//練習：刪除字符數組中的某個字符？
//刪除
void delchar(char *str, char del){
    char *p = str;
    while (*str != '\0') {
        //
        if (*str != del) {
            *p++ = *str;
        }
        str++;
    }
    *p = '\0';
}

void main(){
    char p1[] = "Love";
    delchar(p1, 'o');
    printf("%s\n", p1);
    getchar();
}

文檔：

函數名: stpcpy
功 能: 拷貝一個字符串到另一個
用 法: char *stpcpy(char *destin, char *source);
程序例:

include <stdio.h>

include <string.h>

int main(void)
{
char string[10];
char *str1 = "abcdefghi";
stpcpy(string, str1);
printf("%sn", string);
return 0;
}

函數名: strcat
功 能: 字符串拼接函數
用 法: char *strcat(char *destin, char *source);
程序例:

include <string.h>

include <stdio.h>

int main(void)
{
char destination[25];
char *blank = " ", *c = "C++", *Borland = "Borland";
strcpy(destination, Borland);
strcat(destination, blank);
strcat(destination, c);
printf("%sn", destination);
return 0;
}

函數名: strchr
功 能: 在一個串中查找給定字符的第一個匹配之處
用 法: char *strchr(char *str, char c);
程序例:

include <string.h>

include <stdio.h>

int main(void)
{
char string[15];
char *ptr, c = 'r';
strcpy(string, "This is a string");
ptr = strchr(string, c);
if (ptr)
printf("The character %c is at position: %dn", c, ptr-string);
else
printf("The character was not foundn");
return 0;
}

函數名: strcmp
功 能: 串比較
用 法: int strcmp(char *str1, char *str2);
看Asic碼，str1>str2，返回值 > 0；兩串相等，返回0
程序例:

include <string.h>

include <stdio.h>

int main(void)
{
char *buf1 = "aaa", *buf2 = "bbb", *buf3 = "ccc";
int ptr;
ptr = strcmp(buf2, buf1);
if (ptr > 0)
printf("buffer 2 is greater than buffer 1n");
else
printf("buffer 2 is less than buffer 1n");
ptr = strcmp(buf2, buf3);
if (ptr > 0)
printf("buffer 2 is greater than buffer 3n");
else
printf("buffer 2 is less than buffer 3n");
return 0;
}

函數名: strncmpi
功 能: 將一個串中的一部分與另一個串比較, 不管大小寫
用 法: int strncmpi(char *str1, char *str2, unsigned maxlen);
程序例:

include <string.h>

include <stdio.h>

int main(void)
{
char *buf1 = "BBB", *buf2 = "bbb";
int ptr;
ptr = strcmpi(buf2, buf1);
if (ptr > 0)
printf("buffer 2 is greater than buffer 1n");
if (ptr < 0)
printf("buffer 2 is less than buffer 1n");
if (ptr == 0)
printf("buffer 2 equals buffer 1n");
return 0;
}

函數名: strcpy
功 能: 串拷貝
用 法: char *strcpy(char *str1, char *str2);
程序例:

include <stdio.h>

include <string.h>

int main(void)
{
char string[10];
char *str1 = "abcdefghi";
strcpy(string, str1);
printf("%sn", string);
return 0;
}

函數名: strcspn
功 能: 在串中查找第一個給定字符集內容的段
用 法: int strcspn(char *str1, char *str2);
程序例:

include <stdio.h>

include <string.h>

include <alloc.h>

int main(void)
{
char *string1 = "1234567890";
char *string2 = "747DC8";
int length;
length = strcspn(string1, string2);
printf("Character where strings intersect is at position %dn", length);
return 0;
}

函數名: strdup
功 能: 將串拷貝到新建的位置處
用 法: char *strdup(char *str);
程序例:

include <stdio.h>

include <string.h>

include <alloc.h>

int main(void)
{
char *dup_str, *string = "abcde";
dup_str = strdup(string);
printf("%sn", dup_str);
free(dup_str);
return 0;
}

函數名: stricmp
功 能: 以大小寫不敏感方式比較兩個串
用 法: int stricmp(char *str1, char *str2);
程序例:

include <string.h>

include <stdio.h>

int main(void)
{
char *buf1 = "BBB", *buf2 = "bbb";
int ptr;
ptr = stricmp(buf2, buf1);
if (ptr > 0)
printf("buffer 2 is greater than buffer 1n");
if (ptr < 0)
printf("buffer 2 is less than buffer 1n");
if (ptr == 0)
printf("buffer 2 equals buffer 1n");
return 0;
}

函數名: strerror
功 能: 返回指向錯誤信息字符串的指針
用 法: char *strerror(int errnum);
程序例:

include <stdio.h>

include <errno.h>

int main(void)
{
char *buffer;
buffer = strerror(errno);
printf("Error: %sn", buffer);
return 0;
}

函數名: strcmpi
功 能: 將一個串與另一個比較, 不管大小寫
用 法: int strcmpi(char *str1, char *str2);
程序例:

include <string.h>

include <stdio.h>

int main(void)
{
char *buf1 = "BBB", *buf2 = "bbb";
int ptr;
ptr = strcmpi(buf2, buf1);
if (ptr > 0)
printf("buffer 2 is greater than buffer 1n");
if (ptr < 0)
printf("buffer 2 is less than buffer 1n");
if (ptr == 0)
printf("buffer 2 equals buffer 1n");
return 0;
}

函數名: strncmp
功 能: 串比較
用 法: int strncmp(char *str1, char *str2, int maxlen);
程序例:

include <string.h>

include <stdio.h>

int main(void)
{
char *buf1 = "aaabbb", *buf2 = "bbbccc", *buf3 = "ccc";
int ptr;
ptr = strncmp(buf2,buf1,3);
if (ptr > 0)
printf("buffer 2 is greater than buffer 1n");
else
printf("buffer 2 is less than buffer 1n");
ptr = strncmp(buf2,buf3,3);
if (ptr > 0)
printf("buffer 2 is greater than buffer 3n");
else
printf("buffer 2 is less than buffer 3n");
return(0);
}

函數名: strncmpi
功 能: 把串中的一部分與另一串中的一部分比較, 不管大小寫
用 法: int strncmpi(char *str1, char *str2);
程序例:

include <string.h>

include <stdio.h>

int main(void)
{
char *buf1 = "BBBccc", *buf2 = "bbbccc";
int ptr;
ptr = strncmpi(buf2,buf1,3);
if (ptr > 0)
printf("buffer 2 is greater than buffer 1n");
if (ptr < 0)
printf("buffer 2 is less than buffer 1n");
if (ptr == 0)
printf("buffer 2 equals buffer 1n");
return 0;
}

函數名: strncpy
功 能: 串拷貝
用 法: char *strncpy(char *destin, char *source, int maxlen);
程序例:

include <stdio.h>

include <string.h>

int main(void)
{
char string[10];
char *str1 = "abcdefghi";
strncpy(string, str1, 3);
string[3] = '';
printf("%sn", string);
return 0;
}

函數名: strnicmp
功 能: 不注重大小寫地比較兩個串
用 法: int strnicmp(char *str1, char *str2, unsigned maxlen);
程序例:

include <string.h>

include <stdio.h>

int main(void)
{
char *buf1 = "BBBccc", *buf2 = "bbbccc";
int ptr;
ptr = strnicmp(buf2, buf1, 3);
if (ptr > 0)
printf("buffer 2 is greater than buffer 1n");
if (ptr < 0)
printf("buffer 2 is less than buffer 1n");
if (ptr == 0)
printf("buffer 2 equals buffer 1n");
return 0;
}

函數名: strnset
功 能: 將一個串中的所有字符都設為指定字符
用 法: char *strnset(char *str, char ch, unsigned n);
程序例:

include <stdio.h>

include <string.h>

int main(void)
{
char *string = "abcdefghijklmnopqrstuvwxyz";
char letter = 'x';
printf("string before strnset: %sn", string);
strnset(string, letter, 13);
printf("string after strnset: %sn", string);
return 0;
}

函數名: strpbrk
功 能: 在串中查找給定字符集中的字符
用 法: char *strpbrk(char *str1, char *str2);
程序例:

include <stdio.h>

include <string.h>

int main(void)
{
char *string1 = "abcdefghijklmnopqrstuvwxyz";
char *string2 = "onm";
char *ptr;
ptr = strpbrk(string1, string2);
if (ptr)
printf("strpbrk found first character: %cn", *ptr);
else
printf("strpbrk didn't find character in setn");
return 0;
}

函數名: strrchr
功 能: 在串中查找指定字符的最后一個出現
用 法: char *strrchr(char *str, char c);
程序例:

include <string.h>

include <stdio.h>

int main(void)
{
char string[15];
char *ptr, c = 'r';
strcpy(string, "This is a string");
ptr = strrchr(string, c);
if (ptr)
printf("The character %c is at position: %dn", c, ptr-string);
else
printf("The character was not foundn");
return 0;
}

函數名: strrev
功 能: 串倒轉
用 法: char *strrev(char *str);
程序例:

include <string.h>

include <stdio.h>

int main(void)
{
char *forward = "string";
printf("Before strrev(): %sn", forward);
strrev(forward);
printf("After strrev(): %sn", forward);
return 0;
}

函數名: strset
功 能: 將一個串中的所有字符都設為指定字符
用 法: char *strset(char *str, char c);
程序例:

include <stdio.h>

include <string.h>

int main(void)
{
char string[10] = "123456789";
char symbol = 'c';
printf("Before strset(): %sn", string);
strset(string, symbol);
printf("After strset(): %sn", string);
return 0;
}

函數名: strspn
功 能: 在串中查找指定字符集的子集的第一次出現
用 法: int strspn(char *str1, char *str2);
程序例:

include <stdio.h>

include <string.h>

include <alloc.h>

int main(void)
{
char *string1 = "1234567890";
char *string2 = "123DC8";
int length;
length = strspn(string1, string2);
printf("Character where strings differ is at position %dn", length);
return 0;
}

函數名: strstr
功 能: 在串中查找指定字符串的第一次出現
用 法: char *strstr(char *str1, char *str2);
程序例:

include <stdio.h>

include <string.h>

int main(void)
{
char *str1 = "Borland International", *str2 = "nation", *ptr;
ptr = strstr(str1, str2);
printf("The substring is: %sn", ptr);
return 0;
}

函數名: strtod
功 能: 將字符串轉換為double型值
用 法: double strtod(char *str, char **endptr);
程序例:

include <stdio.h>

include <stdlib.h>

int main(void)
{
char input[80], *endptr;
double value;
printf("Enter a floating point number:");
gets(input);
value = strtod(input, &endptr);
printf("The string is %s the number is %lfn", input, value);
return 0;
}

函數名: strtok
功 能: 查找由在第二個串中指定的分界符分隔開的單詞
用 法: char *strtok(char *str1, char *str2);
程序例:

include <string.h>

include <stdio.h>

int main(void)
{
char input[16] = "abc,d";
char p;
/ strtok places a NULL terminator
in front of the token, if found /
p = strtok(input, ",");
if (p) printf("%sn", p);
/ A second call to strtok using a NULL
as the first parameter returns a pointer
to the character following the token */
p = strtok(NULL, ",");
if (p) printf("%sn", p);
return 0;
}

函數名: strtol
功 能: 將串轉換為長整數
用 法: long strtol(char *str, char **endptr, int base);
程序例:

include <stdlib.h>

include <stdio.h>

int main(void)
{
char *string = "87654321", endptr;
long lnumber;
/ strtol converts string to long integer */
lnumber = strtol(string, &endptr, 10);
printf("string = %s long = %ldn", string, lnumber);
return 0;
}

函數名: strupr
功 能: 將串中的小寫字母轉換為大寫字母
用 法: char *strupr(char *str);
程序例:

include <stdio.h>

include <string.h>

int main(void)
{
char *string = "abcdefghijklmnopqrstuvwxyz", ptr;
/ converts string to upper case characters */
ptr = strupr(string);
printf("%sn", ptr);
return 0;
}

函數名: swab
功 能: 交換字節
用 法: void swab (char *from, char *to, int nbytes);
程序例:

include <stdlib.h>

include <stdio.h>

include <string.h>

char source[15] = "rFna koBlrna d";
char target[15];
int main(void)
{
swab(source, target, strlen(source));
printf("This is target: %sn", target);
return 0;
}

PS:isalpha()是字符函數，不是字符串函數，

isalpha

原型：extern int isalpha(int c);

用法：#include <ctype.h>

功能：判斷字符c是否為英文字母

說明：當c為英文字母a-z或A-Z時，返回非零值，否則返回零。

舉例：

  // isalpha.c
  
  #include <syslib.h>
  #include <ctype.h>
  #include <stdio.h>

  main()
  {
    int c;
    
    clrscr();        // clear screen
    printf("Press a key");
    for(;;)
    {
      c=getchar();
      clrscr();
      printf("%c: %s letter",c,isalpha(c)?"is":"not");
    }
    return 0; // just to avoid warnings by compiler
  }