用数字6代替数字5

Question

i want to replace 5 with 6 and print the number

i want to replace 5 with 6 and print the number but i cant understand whats wrong in my code. for instance when i give 200 the output should be same ie 200 but it gives 199 and when i give 205 as input instead of giving 206 as output it gives 205 itself.

#include<stdio.h>
#include<math.h>
int main()
{
    int n,i=0,r,sum=0;
    while(1){
        printf("\nenter no\n");
        scanf("%d",&n);
        while(n>0)
        {
            r=n%10;
            printf("r is= %d\n",r);
            if(r==5)
            {
                r=6;
            }
            sum=sum+(r*pow(10,i));
            n=n/10;
            i++;
        }
        printf("new no is:\t %d",sum);
        sum=0;i=0;
    }
    return 0;
}

Answer 1

Like others have noted, it's a floating-point arithmetic problem, the value pow outputs is little bit less than the desired value (ie. getting 199.999999 instead of 200, so it gets rounded to 199). There is a similar post about this behaviour.

Anyway, if you just want it to work you could replace this line:

sum=sum+(r*pow(10,i));

with:

 sum=sum+(r*(int)(pow(10,i)+0.5));

and it will get rounded just right. Once again, this is just a fast solution that'll help you make the program work, as I assume you are a begginer in C.

But I STRONGLY advise you to read about the floating-point arithmetic behaviour in programming languages, and why using pow on integers is a bad practice in C/C++.