"# string output in reverse order
Realize the logic, obtain the string length through strlen, and then perform cross assignment through len / 2. It should be noted here that it is not necessary to consider whether len is odd or even.
If len is an odd number, the last character does not need to be in reverse order. If it is an even number, the last two characters are in reverse order.
#include""stdio.h""
voidrechange_ str(char*str)
{
inti,len;
chartmp;
if(NULL==str){
return;
}
len=strlen(str);
for(i=0; i< len/2; i ++) {
tmp = str[i];
str[i] = str[len-i-1];
str[len-i-1] = tmp;
}
}
int main(void)
{
char str[20] = "" hello,world"";
printf(""%s
"",str);
rechange_ str(str);
printf(""%s
"",str);
return(0);
}
Program output
hello,world
dlrow,olleh
--------------------------------
Processexitedafter0.02841secondswithreturnvalue0
Please press any key to continue
#Integer to string
Implementation logic. Each integer can be converted to hexadecimal. From one bit to ten bits, the hundred bits can be obtained through the% operation plus / operation, and then a character array is used to save 0-f.
Use the corresponding value of a single digit to convert into characters. Note that the converted string is reverse. Also consider how to deal with the incoming negative number, and then flip the string to complete the last whole operation
The following code needs to be studied. You'd better run it yourself.
#include""stdio.h""
char*sky_ itoa(intvalue,char*str,unsignedintradix)
{
charlist[]=""0123456789ABCDEF"";
unsignedinttmp_ value;
inti,j,k;
if(NULL==str){
returnNULL;
}
if(2!= radix&&8!= radix&&10!= radix&&16!= radix){
returnNULL;
}
i=0;
k=0;
if(radix==10&&value< 0) {
tmp_ value = ( unsigned int)(0 - value);
str[i++] = '-';
k=1;
}else{
tmp_ value=(unsignedint)value;
}
do{
str[i++]=list[tmp_ value%radix];
tmp_ value/=radix;
}while(tmp_ value);
str[i]='';
//Flip
chartmp;
for(j=k; j< ( i+k)/2; j++) {
tmp = str[j];
str[j] = str[i+k-j-1];
str[i+k-j-1] = tmp;
}
returnstr;
}
intmain(void)
{
inta=1254545;
charstr[100]={0};
printf(""%s
"",sky_ itoa(a,str,2));
printf(""%s
"",sky_ itoa(a,str,8));
printf(""%s
"",sky_ itoa(a,str,10));
printf(""%s
"",sky_ itoa(a,str,16));
return(0);
}
Program output
100110010010010010001
four million six hundred and twenty-two thousand two hundred and twenty-one
one million two hundred and fifty-four thousand five hundred and forty-five
one hundred and thirty-two thousand four hundred and ninety-one
--------------------------------
Processexitedafter0.02963secondswithreturnvalue0
Please press any key to continue
#String copy
Implement logic and assign values one by one until '' stops
#include""stdio.h""
char*sky_ strcpy(char*dst,constchar*str)
{
if(NULL==dst||NULL==str){
returnNULL;
}
char*ret=dst;
while(*str!=''){
*dst++=*str++;
}
returnret;
}
intmain(void)
{
charstr_ 1[100]=""hello,world"";
charstr[100]={0};
sky_ strcpy(str,str_ 1);
printf(""str_ 1:%s
"",str_ 1);
printf(""str:%s
"",str);
return(0);
}
Program output
str_ 1:hello,world
str:hello,world
--------------------------------
Processexitedafter0.03334secondswithreturnvalue0
Please press any key to continue
#String comparison
1. If the normal comparison is the same, implement the logic to judge whether the string length is the same. If it is the same, compare the characters one by one
#include""stdio.h""
intsky_ strcmp(char*dst,char*str)
{
inti,len;
if(NULL==dst||NULL==str){
return0;
}
if(strlen(dst)!= strlen(str)){
return0;
}
len=strlen(dst);
for(i=0; i< len; i++) {
if(*dst++!=* str++){
return0;
}
}
return1;
}
intmain(void)
{
charstr_ 1[100]=""hello,world"";
charstr_ 2[100]=""hello,world"";
charstr[100]=""adfs"";
printf(""%d
"",sky_ strcmp(str_ 1,str));
printf(""%d
"",sky_ strcmp(str_ 1,str_ 2));
return(0);
}
Program output
0
one
--------------------------------
Processexitedafter0.02802secondswithreturnvalue0
Please press any key to continue
2. Ignore case string comparison
Implement logic. When comparing characters, they can be uniformly converted to uppercase or lowercase, and then compared. It is no different from normal comparison
#include""stdio.h""
#defineCONVERT(c)(((c)>='A'&&(c)<= ' Z') ? (( c) - ' A' + ' a') : ( c))
intsky_ strcmp(char*dst,char*str)
{
inti,len;
if(NULL==dst||NULL==str){
return0;
}
if(strlen(dst)!= strlen(str)){
return0;
}
len=strlen(dst);
for(i=0; i< len; i++) {
if(CONVERT(*dst)!= CONVERT(*str)){
return0;
}
dst++;
str++;
}
return1;
}
intmain(void)
{
charstr_ 1[100]=""heLlo,world"";
charstr_ 2[100]=""hello,world"";
charstr[100]=""adfs"";
printf(""%d
"",sky_ strcmp(str_ 1,str));
printf(""%d
"",sky_ strcmp(str_ 1,str_ 2));
return(0);
}
Program output
0
one
--------------------------------
Processexitedafter0.04624secondswithreturnvalue0
Please press any key to continue
#Memcpy function implementation
The implementation logic is mainly completed by assigning values one by one
1. Copy coverage is not considered
#include""stdio.h""
#include""string.h""
void*sky_ memecpy(void*dst,constvoid*str,intn)
{
if(NULL==dst||NULL==str||n<= 0) {
returnNULL;
}
char*pdst=(char*)dst;
char*pstr=(char*)str;
while(n--){
*pdst++=*pstr++;
}
returndst;
}
intmain(void)
{
charstr_ 1[100]=""heLlo,world"";
charstr_ 2[100]=""sdfsdfs"";
sky_ memecpy(str_ 2,str_ 1,strlen(str_ 1));
printf(""%s
"",str_ 2);
return(0);
}
Program output
heLlo,world
--------------------------------
Processexitedafter0.02516secondswithreturnvalue0
Please press any key to continue
2. Consider copy coverage
Copy overwrite is a problem we need to pay attention to when copying strings. In my following example program, there is a problem when using the first function, and there is no problem when using the second function.
The reason is that the addresses of our source string and destination string are the same. We want to move the string back one position, but there is actually a problem.
#include""stdio.h""
#include""string.h""
void*sky_ memecpy_ 1(void*dst,constvoid*str,intn)
{
if(NULL==dst||NULL==str||n<= 0) {
returnNULL;
}
char*pdst=(char*)dst;
char*pstr=(char*)str;
while(n--){
*pdst++=*pstr++;
}
returndst;
}
void*sky_ memecpy(void*dst,constvoid*str,intn)
{
if(NULL==dst||NULL==str||n<= 0) {
returnNULL;
}
char*pdst=(char*)dst;
char*pstr=(char*)str;
if(pdst>pstr&&pdst< pstr + n) {
pdst = pdst + n - 1;
pstr = pstr + n - 1;
while(n--){
*pdst--=*pstr--;
}
}else{
while(n--){
*pdst++=*pstr++;
}
}
returndst;
}
intmain(void)
{
charstr_ 1[100]=""heLlo,world"";
charstr_ 2[100]=""heLlo,world"";
sky_ memecpy_ 1(str_ 1+1,str_ 1,strlen(str_ 1));
printf(""%s
"",str_ 1);
sky_ memecpy(str_ 2+1,str_ 2,strlen(str_ 2));
printf(""%s
"",str_ 2);
return(0);
}
Program output
hhhhhhhhhhhh
hheLlo,world
-------------------
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