C language (Itoa function)

 itoa Function is to convert a number into its corresponding hexadecimal number format

for example   -10 To 10 Base number -10

           4 To 2 Base number   100     

The main idea is   The only special case is the decimal form of negative numbers , As long as it is specially treated

The method of finding Radix is generally rolling division （ Be careful ： The data obtained here is inverse , Need inverse ）

#include<stdio.h>
#include<assert.h>
char* my_itoa(int value,char* buff,unsigned int radix) {
	assert(buff!=NULL&&radix>1);// Assertion buff It is not empty and the decimal number is greater than 1
	char index[] = "0123456789abcdefghijklmnopqrstuvwxyz";
    // Define character groups , It is used to represent various numbers 
	unsigned int temp = (unsigned int)value;// There will be a sign value Value is strongly converted to unsigned 
	int flag = value < 0 && radix == 10 ? 1 : 0;// Judge whether it is a decimal system （ Special treatment ）
	if (flag == 1) {// It is judged to be decimal and negative 
		buff[0] = '-';// The first element is a negative sign 
		temp *= -1;// take value Become a positive number 
	}
	int i = flag;
	for (; temp != 0;i++) {
		buff[i] = index[temp % radix];
		temp /= radix;
	}
	buff[i] = '\0';
    // Because the reverse order is obtained by using the rolling division , So you need to reverse the entire array 
	for (int j = 0; j < (i - flag)/2;j++) {
		int temp = buff[j+flag];
		buff[j + flag] = buff[i - 1 - j];
		buff[i - 1 - j] = temp;
	}
	return buff;
}
int main() {
	char buff[256];
	char* res = my_itoa(11,buff,16);
	printf("%s\n",res);
	return 0;
}

The test case ：（ The first number is the number to be transferred , The second number is a base number ）