Wrong output while running C code [duplicate]

Question

This question already has answers here:

Why are these constructs using pre and post-increment undefined behavior? (14 answers)

Closed 2 years ago.

Possible Duplicate:
Parameter evaluation order before a function calling in C

For the below code I expected the output to be 20 and 76 but instead 75 and 21 is comming as output .Please explain why is so.

    #include<stdio.h>

    unsigned func(unsigned n)
    {

       unsigned int a =1 ;        
       static unsigned int b=2;        
       a+=b; b+=a;        
       {

         unsigned int a=3;        
         a+=b; b+=a;        
       }
       //printf("%d %d ",a,b);
       return (n+a+b);        
    }
    int main()
    {
        printf("%d %d\n",func(4),func(5));
        return 0;
    }

Answer 1

The order of evaluation of expression is unspecified behaviour hence func(4) and func(5) may be called in different order as you supposed to

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Parameter evaluation order before a function calling in C

Answer 2

func(5) is getting executed first :

Values of variables after executing func(5) :

a = 3
b = 13
func(5) = 21

Since, b is static, the values after executing func(4):

a = 14
b = 57
func(4) = 75