Question

Very similar to Python or R. The examples below should be self-explanatory.

if-else

// Interpretation of grades by Asian parent
if (grade == 'A') {
    printf("Acceptable\n");
} else if (grade == 'B') {
    printf("Bad\n");
} else if (grade == 'C') {
    printf("Catastrophe\n");
} else if (grade == 'D') {
    printf("Disowned\n");
} else {
    printf("Missing child report filed with local police\n")
}

for, while, do

// Looping variants

// the for loop in C consists of the keyword for followed by
// (initializing statement; loop condition statement; loop update statement)
// followed by the body of the loop in curly braces
int arr[3] = {1, 2, 3};
for (int i=0; i<sizeof(arr)/sizeof(arr[0]); i++) {
    printf("%d\n", i);
}

// the while loop
int i = 3;
while (i > 0) {
    i--;
}

// the do loop is similar to the while loop but will execute the body at least once
int i = 3;
do {
    i==;
} while (i > 0);

The C standard does not require braces if the body is a singel line, but I think it is safer to always include them. Note that whitespace is not significant in C (unlike Python), so

int i = 10;
while (i > 0)
    i--;
    i++;

actually means

int i = 10;
while (i > 0) {
    i--;
}
i++;

and the use of braces even for single statement bodies prevnets such errors.