CODEWITHSUNDEEP
ccharmaxlimitansi-c
user1717828
user1717828

Reputation: 7223

Finding max value of char in C

I am finding the maximum value of a char by simple addition and testing for when the number goes negative:

#include<stdio.h>

/*find max value of char by adding*/
int main(){
  char c = 1;

  while(c + 1 > 0)
    ++c;

  printf("Max c = %d\n",(int)c);  /*outputs Max c = -128*/
  return 0;
}

The while loop tests ahead, so the first time c+1 is negative it breaks and we print the value of c. However, the programming is outputting the negative number!

Why doesn't this program output 127?

Upvotes: 5

Views: 7770

Answers (2)

Danilo Piazzalunga
Danilo Piazzalunga

Reputation: 7802

Signed integer overflow is undefined behavior. This means that a conforming C compiler is allowed to change c + 1 > 0 to true, because the addition "cannot" overflow.

This means that your program could legitimately be compiled to an endless loop.

Upvotes: 1

bgoldst
bgoldst

Reputation: 35324

There is an implicit cast occurring in the while conditional which is causing the comparison to work on ints rather than chars.

If you change it to

while((char)(c + 1) > 0)
    ++c;

then it will print 127.

Upvotes: 5

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