C provides an extremely useful statement called
if lets your programs make decisions and execute certain statements based on the results of those decisions. By testing contents of variables, your programs can produce different output, given different input.
This chapter also describes relational operators. Combined with
if, relational operators make C a powerful data-processing language. Computers would really be boring if they couldn’t test data; they would be little more than calculators if they had no capability to decide courses of action based on data.
if statement works just like it does in spoken language: ...