c - Dynamically allocating in main() VS in a funtion -

int foo(int *p){     p = malloc(sizeof(int));     *p = 20; }  int main(){     int a;     int *x;     x = &a;     foo(x);     printf("%d \n", a);     return 0; } 

so i'm trying point @ a , set value of x pointing 20. whenever allocate pointer in function random number being printed. know why happens compared allocating in main()?

you don't want allocate in foo function @ all. doing:

void foo(int p) {     p = 2;     printf("%d\n", p); }  int main() {     int a=1;     foo(a);     return 0; } 

and asking why didn't print 1. answer is, you're writing on pointer a, no longer have pointer when *p = 20;.