Control Statements
A program consists of a number of statements which are usually executed in sequence. Programs can be much more powerful if we can control the order in which statements are run.
Statements fall into three general types:
- Assignment, where values, usually the results of calculations, are stored in variables.
- Input / Output, data is read in or printed out.
- Control, the program makes a decision about what to do next.
This section will discuss the use of control statements in C. We will show how they can be used to write powerful programs by;
- Repeating important sections of the program.
- Selecting between optional sections of a program.
The if else Statement
This is used to decide whether to do something at a special point, or to decide between two courses of action.
The following test decides whether a student has passed an exam with a pass mark of 45
if (result >= 45)
printf("Pass\n");
else
printf("Fail\n");
It is possible to use the if part without the else.
if (temperature < 0)
print("Frozen\n");
Each version consists of a test, in the bracketed statement following the if. If the test is true then the next statement is obeyed. If it is false then the statement following the else is obeyed if present. After this, the rest of the program continues as normal.
If we wish to have more than one statement following the if or the else, they should be grouped together between curly brackets. Such a grouping is called a compound statement or a block.
if (result >= 45)
{ printf("Passed\n");
printf("Congratulations\n");
}
else
{ printf("Failed\n");
printf("Better Luck Next Time\n");
}
Sometimes we wish to make a multi-way decision based on several conditions. The most general way of doing this is by using the else if variant on the if statement.
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