Read this.
A development process

This is your assignment.
Format Input
The first line will be an integer T, the number of test cases.
Each test case will contain an integer N, the starting number.

Format Output
Print “Case #X:” on the first line of each test case.
Then print the countdown each on their own line.
Look at each statement in turn, and just write the code for that.
So.
Code:
// The first line will be an integer T, the number of test cases.
scanf("%d",&numTestCases);
for ( int i = 1 ; i <= numTestCases ; i++ ) {
    // Print “Case #X:” on the first line of each test case.
    printf("Case #%d:\n", i);
}
Then it becomes say
Code:
// The first line will be an integer T, the number of test cases.
scanf("%d",&numTestCases);
for ( int i = 1 ; i <= numTestCases ; i++ ) {
    // Print “Case #X:” on the first line of each test case.
    printf("Case #%d:\n", i);
    // Each test case will contain an integer N, the starting number.
    scanf("%d",&startNumber);
    // Then print the countdown each on their own line.
    for ( int c = startNumber ; c >= 1 ; c-- ) {
        printf("%d\n", c);
    }
}
Each step of the way, you add one more requirement to the program.