1.不使用庫函數將整數轉換爲字符串
C語言提供了將幾個標準庫函數,可以將任意類型的(整形、浮點型、長整形)的數字轉換爲字符串
itoa():將整形值轉換爲字符串
ltoa();將長整形轉換爲字符串
ultoa();將無符號長整形轉換爲字符串
gcvt();將浮點數轉換爲字符串,取四捨五入
ecvt();將雙精度浮點數轉換爲字符串,轉換結果中不包含十進制小數點
fcvt();將指定位數轉換精度
還可以使用sprintf系類函數把數字轉換爲字符串,這種方式比itoa系列函數速度慢
#include<stdio.h>
#include<iostream>
using namespace std;
void int2str(int n, char*str)
{
char buf[10] = {0}; //臨時數組
int i = 0; //臨時數組buf的下標
int j = 0; //str的下標
int len=0;
int temp = n < 0 ? -n : n; //取數字n的絕對值
if (n < 0) //首先對負數做處理
{
str[j] = '-';
j++;
}
//將數字倒序放在臨時數組
while (temp)
{
buf[i] = temp%10 + '0';
i++;
temp /= 10;
}
//轉換
len = i - 1;
while (len>=0)
{
str[j] = buf[len];
j++;
len--;
}
str[j] = '\0';
}
int main()
{
int num;
char p[10];
cout << "please input the number:" << endl;
cin >> num;
int2str(num, p);
cout << "ouput: " << p << endl;
return 0;
}
please input the number:
-1234
ouput: -1234
2.不使用庫函數將字符串轉換爲數字
與數字轉換爲字符串類似,C/C++提供了幾個標準的庫函數,可以將字符串轉換爲任意類型(整型,長整型,浮點型)的數字。下面列舉其函數
atof();將字符串轉換爲雙精度浮點型值
atoi();將字符串轉換爲整型值
atol();將字符串轉換爲長整型
strtod();將字符串轉換爲雙精度浮點型值,並報告不能被轉換的所有剩下數字
strtol();將字符串轉換爲長整型值,並報告不能被轉換的所有剩下的數字
strtoul();將字符串轉換爲無符號長整型,並報告不能被轉換的所有剩下的數字
//2.不使用庫函數將數字符串轉換爲數字
#include<iostream>
using namespace std;
int str2int(const char * str)
{
int temp=0;
const char *ptr = str; //ptr保存str字符串開頭
if (*str == '-' || *str == '+') //如果第一個字符是正負號,則移到下一個字符
{
str++;
}
while (*str != 0)
{
if ((*str < '0') || *str > '9') //如果當前字符不是數字,則退出循環
{
break;
}
temp = temp * 10 + (*str - '0'); //如果當前字符是數字,則計算數值,然後移到下一個字符
str++;
}
if(*ptr=='-') //如果字符串以‘-’開頭,則轉換成其相反數
{
temp = -temp;
}
return temp;
}
int main()
{
int n = 0;
char p[10] = "";
cout << "input: " << endl;
//cin >> p[10];
cin.getline(p, 20);
n = str2int(p);
cout << "output:" << n << endl;
return 0;
}
input:
-1234
output:-1234
3.編程實現strcpy函數
//3.編程實現strcpy函數
#include<stdio.h>
char * strcpy(char * strDest, const char * strSrc)
{
if ((strDest == NULL) || (strSrc == NULL))
{
return NULL;
}
char *strDestCopy = strDest; //保存目標字符串的首地址
int i = 0;
//for (i = 0; strSrc[i] != '\0'; strDest[i] = strSrc[i], i++)
while (strSrc[i]!='\0')
{
strDest[i] = strSrc[i]; //把strSrc字符串的內容複製到strDest中
i++;
}
strDest[i] = '\0'; //加入結束符
return strDestCopy; //返回首地址
}
int main()
{
char strSrc[] = "hello world";
char strDest[20];
strcpy(strDest, strSrc);
printf("strDest:%s\n", strDest);
return 0;
}
strDest:hello world
4.編程實現計算字符串的長度
//4.編程實現計算字符串的長度
#include<stdio.h>
int strlen1(const char* src)
{
if (src == NULL) //判斷src是否有效
{
return 0;
}
int len = 0;
while (*src!='\0')
{
*src++;
len++;
}
return len;
}
int strlen2(const char* src)
{
if (src == NULL) //判斷src是否有效
{
return 0;
}
const char *temp = src; //保存src的首地址
while (*src!='\0')
{
src++;
}
return (src - temp); //返回指針差
}
int main()
{
char p[] = "Hello World!";
printf("Strlen1 len: %d\n", strlen1(p));
printf("Strlen2 len: %d\n", strlen2(p));
return 0;
}
//第二種方法效率更好
Strlen1 len: 12
Strlen2 len: 12
5.編程實現字符串中子串的查找
編寫一個函數,實現strstr,即從一個字符串中,查找另一個字符串的位置,如果輸入strstr("12345","34")返回值爲2,即在2號位置找到字符串34.
#include<stdio.h>
int strstr(const char* src, const char* sub)
{
const char *bp = src; //定義指針bp指向src首地址
const char *sp = sub;
int flag = 0;
const char *temp = src; //定義一個臨時指針temp,暫時先指向src首地址
if (src == NULL || sub == NULL) //判斷src和sub是否有效
{
return 0;
}
while (*src) //遍歷src
{
sub = sp;
while (*src == *sub) //如果src與sub字符相等進入,如果不等,src++
{
src++; //然後src和sbu都加1,比較下一個字符是否相等
sub++;
flag = 1;
if (*sub == '\0') //如果sub結束了,那就是找到了子串
{
return (temp - bp); //輸出子串的位置,bp是首地址,temp存儲的是第一個相等字符的前一個
break; //字符的位置,然後與首地址相減再加1,就得到最終結果
}
}
if (flag == 1) //flag的作用是如果在上一個while循環中src執行了+1,這裏就不需要再執行一次了
{ //所有先對src--,然後在src++
src--;
flag = 0;
}
src++; //src加1,比較下一個字符
temp = src;
if (*src == '\0') //如果src下一個字符是空,那就結束,
{
return 0;
}
}
}
int main()
{
char p[] = "123345";
char q[] = "34";
printf("the position of sub is : %d\n", strstr(p, q));
return 0;
}
the position of sub is : 36.編程判斷字符串是否是迴文,例如“level”是迴文
//6.編程判斷字符串是否是迴文
//例如“level”是迴文
#include<iostream>
using namespace std;
int IsRevStr(char * str)
{
int i, len;
int found = 1; //1表示是迴文,0表示不是迴文
if (str == NULL)
{
return -1;
}
len = strlen(str);
for (i = 0; i < len / 2; i++)
{
if (str[i] != str[len - i - 1]) //不是迴文
{
found = 0;
break;
}
}
return found;
}
int main()
{
char str1[] = "1234321";
char str2[] = "1234221";
int test1 = IsRevStr(str1);
int test2 = IsRevStr(str2);
cout << "str1 is " << (test1 == 1 ? "" : "not ") << "reverse string." << endl;
cout << "str2 is " << (test2 == 1 ? "" : "not ") << "reverse string." << endl;
return 0;
}
str1 is reverse string.
str2 is not reverse string.
7.編程實現stcmp庫函數
對於兩個字符串str1,str2,若相等,則返回0,若str1大於str2,則返回1,若str1小於str2,則返回-1
//7.編程實現stcmp庫函數
//對於兩個字符串str1,str2,若相等,則返回0,若str1大於str2,則返回1,若str1小於str2,則返回-1
#include<iostream>
using namespace std;
int mystrcmp(const char*src, const char* dst)
{
int ret = 0;
while (!(ret=*(unsigned char *)src-*(unsigned char *)dst) && *dst)
{
src++; //循環比較兩個字符串是否相等,如果不等或者dst字符串到了末尾,退出循環,
dst++; //與後面的*dst和*src有一個在就可以,如果src到了結尾,而dst沒到結尾,則!ret=0,同樣會結束循環
}
if (ret < 0)
ret = -1;
else if (ret > 0)
ret = 1;
return ret;
}
int main()
{
char str[10] = "1234567";
char str1[10] = "1234567";
char str2[10] = "12345678";
char str3[10] = "1234566";
int test1 = mystrcmp(str, str1);
int test2 = mystrcmp(str, str2);
int test3 = mystrcmp(str, str3);
cout << "test1 = " << test1 << endl;
cout << "test2 = " << test2 << endl;
cout << "test3 = " << test3 << endl;
return 0;
}
test1 = 0
test2 = -1
test3 = 1
8.編寫字符串反轉函數strrev
如:輸入“abcd”,輸出應爲“dcba”
//8.編寫字符串反轉函數strrev
#include<iostream>
using namespace std;
char* strrev1(char* str) //遍歷字符串
{ //第一個與最後一個交換,依次循環
int len = strlen(str);
char *tmp = new char[len + 1];
strcpy_s(tmp,len+1,str);
for (int i = 0; i < len / 2; i++)
{
char c = tmp[i];
tmp[i] = tmp[len - i-1];
tmp[len - i - 1] = c;
}
return tmp;
}
int main()
{
char * str = "123456";
cout << str << endl;
char* str1 = strrev1(str);
cout << "strrev1(str) = " << str1 << endl;
return 0;
}
123456
strrev1(str) = 654321
9.編程實現任意長度的兩個正整數相加
//9.編程實現任意長度的兩個正整數相加
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<math.h>
char * addBigInt(char * num1, char *num2)
{
int c = 0;// 進位,開始最低進位爲0
int i = strlen(num1)-1; //指向第一個加數的最低位
int j = strlen(num2)-1; //指向第二個加數的最低位
//得到兩個數中較大數的位數並加1,作爲結果的位數
int maxLength = strlen(num1) >= strlen(num2) ? strlen(num1) + 1 : strlen(num2) + 1;
char *rst = (char*)malloc(maxLength + 1); //保存結果
int k;
if (rst == NULL)
{
printf("malloc error\n");
exit(1);
}
rst[maxLength] = '\0'; //字符串最後一位爲'\0';
k = strlen(rst) - 1; //指向結果數組的最低位
while ((i>=0)&&(j>=0))
{
rst[k] = ((num1[i] - '0') + (num2[j] - '0') + c) % 10 + '0';
c = ((num1[i] - '0') + (num2[j] - '0') + c) / 10;
i--;
j--;
k--;
}
while (i>=0)
{
rst[k] = ((num1[i] - '0')+ c) % 10 + '0';
c = ((num1[i] - '0')+ c) / 10;
i--;
k--;
}
while (j>=0)
{
rst[k] = ((num2[j] - '0') + c) % 10 + '0';
c = ((num2[j] - '0') + c) / 10;
j--;
k--;
}
rst[0] = c +'0';
if (rst[0] !='0')
{
return rst;
}
else
{
return rst + 1; //如果最高位等於零,那麼就從結果str的第二個元素開始輸出
}
}
int main()
{
char num1[] = "123";
char num2[] = "996";
char *result = NULL;
result = addBigInt(num1, num2);
printf("%s + %s = %s\n", num1, num2, result);
return 0;
}
123 + 996 = 1119
10.編程實現字符串的循環右移
編寫函數能把一個char組成的字符串循環右移n個,例如原來是“abcdefghi”,如果n=2,移位後應該是“hiabcdefg”
//10.編程實現字符串的循環右移
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
void loopMove(char* str, int n)
{
int i = 0;
char *temp = NULL;
int strLen = strlen(str);
char *head = str;
n = n%strLen;
temp = (char*)malloc(n);
for (i = 0; i < n; i++)
{
temp[i] = head[strLen - n + i];
}
for (i = strLen - 1; i >= n; i--)
{
head[i] = head[i - n];
}
for (i = 0; i < n; i++)
{
head[i] = temp[i];
}
free(temp);
}
int main()
{
char string[] = "abcdefghi";
int steps = 0;
printf("string: %s\n", string);
printf("input steps: ");
scanf_s("%d", &steps);
loopMove(string,steps);
printf("after loopMove %d: %s\n", steps, string);
return 0;
}
string: abcdefghiinput steps: 2
after loopMove 2: hiabcdefg
11.刪除制定長度的字符
例如:假設一個字符串“abcdefg”,如果要從第二個開始(索引爲1),刪除兩個字符,則刪除後的字符串是“adefg”
//11.刪除制定長度的字符
#include<stdio.h>
#include<string.h>
#include<iostream>
using namespace std;
char *deleteChars(char* str, int pos, int len)
{
char *p = str + pos - 1;//指向pos位置字符
int tt = strlen(str); //計算字符長度
if ((pos < 1) || (p - str) > tt) //檢查pos是否大於1,或者pos超出字符串的長度
{
return str;
}
if ((p + len - str) > tt) //len大於pos後剩餘的字符個數
{
while (*p) //那就把pos後面的全部刪掉,直到結束
{
*p = '\0';
p++;
}
}
while (*p && *(p+len))
{
*p = *(p + len);
p++;
}
*p = '\0';
return str;
}
int main()
{
char string[] = "abcdefg";
int pos = 0;
int len = 0;
int steps = 0;
printf("string: %s\n", string);
printf("input pos: ");
cin >> pos;
cout << "input len: ";
cin >> len;
deleteChars(string, pos, len);
printf("after delete %d chars behind pos %d: %s\n", len, pos, string);
return 0;
}
string: abcdefg
input pos: 2
input len: 2
after delete 2 chars behind pos 2: adefg
12.編程實現刪除字符串中所有指定的字符
假設字符串爲“cabcdefcgchci”,把該字符串中所有的字符'c'刪除後,結果爲“abdefghi”
//12.編程實現刪除字符串中所有制定的字符
#include<stdio.h>
#include<iostream>
using namespace std;
char * deleteChar(char* str, char c)
{
char* head = str;
char* p = str;
if (str == NULL) //檢查str的有效性
{
return NULL;
}
while (*p)
{
if (*p != c)
{
*str = *p; //如果不等於c的值,則記錄在str中
str++;
}
p++;
}
*str = '\0'; //結束符
return head;
}
int main()
{
char string[] = "cabcdefcgchci";
char c = 0;
cout << "input char: ";
cin >> c;
cout << "before delete: " << string << endl;
deleteChar(string, c); //刪除所有的c
cout << "after delete: " << string << endl;
return 0;
}
input char: c
before delete: cabcdefcgchci
after delete: abdefghi
13.編程實現庫函數strcat,實現字符串的拼接
//13.編程實現庫函數strcat,拼接函數
#include<stdio.h>
#include<stdlib.h>
#include<iostream>
using namespace std;
char *mystrcat(char *dest, const char* src)
{
char *ret = dest;//保存目的字符串的首地址,以便返回
while (*dest)
{
dest++;
}
while (*src)
{
*dest = *src;
src++;
dest++;
}
*dest = '\0'; //結束符
return ret;
}
int main()
{
char *dest = NULL;
char *str1 = "Hello ";
char *str2 = "World!";
dest = (char*)malloc(256);
*dest = '\0'; //dest裏面是空
mystrcat(mystrcat(dest, str1), str2);
cout << "dest: " << dest << endl;
free(dest);
dest = NULL;
return 0;
}
dest: Hello World!