Replace Bit Field in a 32-bit Register

#include <stdio.h>
#include <stdint.h>
uint32_t replace_bitfield(uint32_t reg,uint32_t val,int pos,int len){
    uint32_t mask=((1U<<len)-1)<<pos;
    reg &= ~mask;
    reg|=(val<<pos)&mask;
    return reg;
}
int main(){
    uint32_t reg,val;
    int pos,len;
    scanf("%u %u %d %d", &reg,&val,&pos,&len);
    printf("%u", replace_bitfield(reg,val,pos,len));
    return 0;
}