Simple scanf like this

#include <stdio.h>

int main() {
    int a;
    int b;
    int c;
    int d;

    printf("input 1st number:\n");
    scanf("%d",&a);
    printf("input 2nd number:\n");
    scanf("%d",&b);
    printf("input 3rd number:\n");
    scanf("%d",&c);

    d=a+b+c;
    printf("result is:%d",d);

    return 0;
}