How to convert a string to a complete integer number in C? - c

Question

I have tried in this way:
//Write a program to find out the reverse order of a given integer
#include <stdio.h>
int
main(void){
//Put variables for the further proceed
int number, quotient=1, remainder;
//Declare a character array
char text[]="princeX";
//Show the message to the user
printf("Enter an integer number :");
//Taking input from the user
scanf("%d",&number);
//To find out the integer number in the reverse order
while(quotient!=0){
quotient=number/10;
remainder=number%10;
number=quotient;
text[6] = remainder + '0';
puts(text);
}
//Converts the string to a whole integer
int numberUpdate=atoi(text);
printf("%d",numberUpdate);
}
I want to achieve: The user will give an integer number then my system will give the reverse order of the given integer number. To accomplish this goal I stored an integer into a character array but not entirely.
For the input: 123456
Output shows like from my code:
prince6
prince5
prince4
prince3
prince2
prince1
Bu my expectation was:
6
5
4
3
2
1
After that, I just simply wanted to print those as an integer. But I could not do that. When I am going to transform these characters into an integer but the output shows zero. Which problem I have been made in my program and how can I solve that puzzle?

Answer 1

The problem started with this line text[6] = remainder + '0';
puts(text); You only changed text[6], which contains ‘X’ and then printed then whole text. That explains why you go
Prince6
Prince5
Prince4
Prince3
Prince2
Prince1
If you want to get the correct output, you should make these changes:
Declare another variable i=0 before while loop.
Replace the problematic lines with text[i] = remainder+‘0’; printf(“%c\n”, text[i]); i++;
You do this because you want to replace all elements within the text. Then you should expect the correct output. These line int numberUpdate=atoi(text);
printf("%d",numberUpdate); will work afterward. It didn’t work at first simply because it couldn’t convert a string with letters into numbers. Since your string only contains number now, everything should work fine as expected.
I hope it was helpful for you, I did my best explaining the issue, I hope you can understand by reading it. :)))

Answer 2

Here you have number to string conversion function.
char *reverse(char *str)
{
char *wrk = str, *end;
if(str)
{
end = str + strlen(str) -1;
while(end > str)
{
char tmp = *wrk;
*wrk++ = *end;
*end-- = tmp;
}
}
return str;
}
char digits[] = "01234567890abcdefghijklmnopqrstxyvwz";
char *convert(char *buff, unsigned long long val, int radix)
{
char *tmp = buff;
if(radix > sizeof(digits) - 1 || radix < 2) return NULL;
while(val)
{
*tmp++ = digits[val % radix];
val /= radix;
}
*tmp = 0;
return reverse(buff);
}
int main(void)
{
char str[30];
printf("decimal: %s\n", convert(str, 345676, 10));
printf("binary: %s\n", convert(str, 345676, 2));
printf("octal: %s\n", convert(str, 345676, 8));
printf("hex: %s\n", convert(str, 345676, 16));
printf("Base 5: %s\n", convert(str, 345676, 5));
printf("Base 29: %s\n", convert(str, 345676, 29));
}
https://godbolt.org/z/6Ge6bs