a Write program that declares a structure to store country name and population in millions. It defines two structure variables and inputs values. It passes both variables to a function that shows the record of the country with more population.

To write a program that accomplishes the given task, you will need to follow these steps:

1. Declare a structure to store the country's name and its population in millions. Let's call this structure "Country".

```c
struct Country {
char name[50];
int population;
};
```

2. Define two structure variables, let's call them "country1" and "country2", of the newly declared "Country" structure.

```c
struct Country country1, country2;
```

3. Input values for both of the structure variables using something like `scanf` or any other method you prefer.

```c
printf("Enter the name of the first country: ");
scanf("%s", country1.name);

printf("Enter the population of the first country (in millions): ");
scanf("%d", &country1.population);

printf("Enter the name of the second country: ");
scanf("%s", country2.name);

printf("Enter the population of the second country (in millions): ");
scanf("%d", &country2.population);
```

4. Create a function, let's call it "showCountryWithMorePopulation", that takes the two country structure variables as arguments and compares their populations. The function will display the record of the country with the higher population.

```c
void showCountryWithMorePopulation(struct Country country1, struct Country country2) {
if (country1.population > country2.population) {
printf("%s has a higher population with %d million people.\n", country1.name, country1.population);
} else if (country2.population > country1.population) {
printf("%s has a higher population with %d million people.\n", country2.name, country2.population);
} else {
printf("Both countries have the same population of %d million people.\n", country1.population);
}
}
```

5. Finally, call the "showCountryWithMorePopulation" function, passing the two country structure variables as arguments.

```c
showCountryWithMorePopulation(country1, country2);
```

Here's the complete program:

```c
#include <stdio.h>

struct Country {
char name[50];
int population;
};

void showCountryWithMorePopulation(struct Country country1, struct Country country2) {
if (country1.population > country2.population) {
printf("%s has a higher population with %d million people.\n", country1.name, country1.population);
} else if (country2.population > country1.population) {
printf("%s has a higher population with %d million people.\n", country2.name, country2.population);
} else {
printf("Both countries have the same population of %d million people.\n", country1.population);
}
}

int main() {
struct Country country1, country2;

printf("Enter the name of the first country: ");
scanf("%s", country1.name);

printf("Enter the population of the first country (in millions): ");
scanf("%d", &country1.population);

printf("Enter the name of the second country: ");
scanf("%s", country2.name);

printf("Enter the population of the second country (in millions): ");
scanf("%d", &country2.population);

showCountryWithMorePopulation(country1, country2);

return 0;
}
```

This program will display the country with the higher population.