Answer:
#include <stdio.h>
#include <math.h>
int main(){
 float x1,x2,y1,y2,distance;
 printf("x1: "); scanf("%f", &x1);
 printf("y1: "); scanf("%f", &y1);
 printf("x2: "); scanf("%f", &x2);
 printf("y2: "); scanf("%f", &y2);
 distance = sqrt((x1 - x2)*(x1 - x2) + (y1 - y2)*(y1 - y2));
 printf("Distance: %f", distance);
 return 0;
}
Step-by-step explanation:
This line declares all required variable (i.e. the coordinates and the distance)
 float x1,x2,y1,y2,distance;
The next four line prompt and get input for the coordinates
 printf("x1: "); scanf("%f", &x1);
 printf("y1: "); scanf("%f", &y1);
 printf("x2: "); scanf("%f", &x2);
 printf("y2: "); scanf("%f", &y2);
This calculates the distance
 distance = sqrt((x1 - x2)*(x1 - x2) + (y1 - y2)*(y1 - y2));
This prints the calculated distance
 printf("Distance: %f", distance);
See attachment for sample runs